Here's some research on the subject, especially highlighting the difference between "the day of YHWH" and "the day of the Lord [Christ]" of the NT, something the Society sometimes ignore. Sorry it's somewhat longwinded, but it's quite comprehensive:
In the LXX and CGS we encounter the phrase ?μ?ρα κυρ?ου “day of the Lord”. Contrary to common expectation, this phrase cannot always be equated with the “day of Jehovah”, i.e., Judgement Day. During this critical period, Jehovah will manifest his glory and might, destroy his enemies, and bring salvation to his people. This is an accute crisis, whereas “Christ’s day”, closely linked to his parousia, consists of an age or epoch. The following discussion has been extracted from TDOT, TLOT, and TDNT.
Jehovah’s day
The special period of time, not twenty-four hours, when Jehovah actively manifests himself against his enemies and in behalf of his people. With divine judgment executed against the wicked, Jehovah of armies comes off victorious over his opposers during this day. It is also a time of salvation and deliverance for the righteous, the day in which Jehovah himself is highly exalted as the Supreme One. Thus, in a double way it is uniquely and exclusively Jehovah’s great day.
Jehovah God is lord of time, not only because he created the constant alternation between day and night, thus laying the foundation for the course of history, but because he also intervenes in the course of history. In the context of the theology of history, the most important expression of his activity is the genitive phrase yôm yhwh “the day of Jehovah”. When Jehovah is the nomen rectum associated with yôm he has a time to act, a time to intervene in “history”; what will take place then, he alone determines. The relative chronology is necessarily not uniquely defined (e.g., future), being defined in each instance by usage and context; but the future is most common. The most important element, however, is God’s acts. During this period, He will manifest his glory and might, destroy his enemies, and bring salvation to his people.
Considerations of the significance of the expression yôm yhwh should pose the question of the meaning of the word yôm in this phrase before posing the question of the origin and development of the concept appropriate to tradition-critical examination. Formally, yôm yhwh belongs to a series of gen . combinations in which yôm is qualified by a proper name (see 3d on yôm midyan, etc.; cf. also 3h y e mê gib?â) and thus, in a pregnant, terse idiom refers to a significant event identified by the proper name, emphasizing the experiential character above the pure, rather indeterminate temporal designation (cf. S. Herrmann, Die prophetischen Heilserwartungen im A T [1965], 120f.). The qualitative determinacy of an act of Yahweh can be seen here both in the past (Ezek 13:5; 34:12; Lam 2:22; cf. Ezek 22:24; Lam 1:12; 2:1, 21) and in the future (thus most passages); one may have also originally thought of various “days of Yahweh” (cf. perhaps Job 24:1). “In the context of Israel’s generally future-oriented and preliminary historical thought and its faith in God’s guidance, which was shaped by its God and the nature of his activity in history, this term was increasingly and predominantly shifted to the future and thus only gradually became ‘the’ day of Yahweh that we encounter most and with which we are most familiar” (Preuss, op. cit. 172).
With reference to the concept of a comprehensive day of Yahweh’s judgment, tradition-critical investigation has revealed that the point of departure is not a cultic day of Yahweh, such as the hypothesized enthronement festival of Yahweh (so, among others, S. Mowinckel, Psalmenstudien 2 [1922]; id., NTT 59 [1958]: 1–56, 209–29; J. Lindblom, Prophecy in Ancient Israel [1962], 316ff.), but, in accordance with accompanying concepts, the experience of a historical act of Yahweh on behalf of his people consisting of a victory over God’s enemies. In particular, the traditions of the Yahweh war (→ ?aba?, → hmm) appropriated by the prophets would have influenced the development of expectations for the future (cf. G. von Rad, “Origin of the Concept of the Day of Yahweh,” JSS 4 [1959]: 97–108; id., Theol. 2:119–25; Schunck, op. cit. 320f., 330; with modifications, Preuss, op. cit. 173, 179, who places greater emphasis on the exodus; and H.-M. Lutz, Jahwe, Jerusalem und die Völker [1968], 130–46: “The day of Yahweh is also war, but not only war” [op. cit. 146]; on the relationship between the descriptions of theophany and the day of Yahweh, cf. J. Jeremias, Theophanie [1965], 97–100; according to M. Weiss, “The Origin of the ‘Day of the Lord’—Reconsidered,” HUCA 37 [1966]: 29–60, the expression was reshaped by Amos).
The expression yôm yhwh “the day of Yahweh” occurs in this form only 16x in the HAS, all in the prophets (from the southern kingdom): Isa 13:6, 9; Ezek 13:5; Joel 1:15; 2:1, 11; 3:4(2:31); 4:14(3:14); Amos 5:18[twice], 20; Obad 15; Zeph 1:7, 14[twice]; Mal 3:23(4:5). In three passages the genitive is replaced by le: Isa. 2:12; Ezek. 30:3; and expanded by the addition of ba’, “comes”, Zech 14:1. In eight passages there is an additional qualification: yôm?ebrât yhwh (Ezek. 7:19; Zeph. 1:18) and yôm ?ap yhwh (Zeph. 2:2, 3; Lam. 2:22), “the day of the wrath of Yahweh”; yôm naqam leyhwh (Isa. 34:8), “the day of vengeance of Yahweh” (Jer. 46:10); zeba? yhwh (Zeph. 1:8), “the day of sacrifice of Yahweh”; also yôm mehûmâ…la’donay (Isa. 22:5), “a day of confusion…for the Lord Yahweh.” Apart from Lam. 2:22, which is retrospective, these citations also are from the prophets. Oddly enough, the expression does not occur in Daniel (see TDOT, vol. VI, p. 29).
For the history of the concept, one can refer to the presentations in these studies. The earliest passage is Am. 5:18-20, which states metaphorically that Yahweh has appointed a “day” when he will intervene, from which no one can escape (cf. Wolff, Joel and Amos, Her m, 33f., 255–57): “Woe to you who seek the day of Yahweh? It is darkness and not ligh t!” This “day” will bring the opposite of what people hope for from Yahweh, namely disaster (“darkness”) rather than deliverance (“light”). His speech is a judgment discourse linked with history (v. 27); it constitutes an integral part of his general message of judgment, in which he proved in many ways to be breaking new ground (cf., e.g., what he says about qe?, “end,” of Israel in 8:2). Amos contested the contemporary expectation of salvation: since Israel is positioned with Yahweh’s enemies, it cannot consider itself to be the “remnant” (→ š?r) who will receive salvation on the day of Yahweh; rather, it must experience the extraordinary consequences of the inescapable intervention of Yahweh. The passage in Amos, similar to Isa 2:12–17 (Wildberger, Isa 1–12, C C, 112f.), focuses on only a few individual elements of the concept, in Amos the darkness, in Isaiah, Yahweh’s majesty above all the proud and arrogant. In like fashion, the form and phraseology of Isaiah’s discourse concerning the “day of Yahweh” in Isa. 2:(6-11), 12-17(18-22) is part of his proclamation of judgment for the people in the present day. The same is true in 22:5, where the mention of “day” is followed at once by “a concrete description with reference to his historical moment.” The “day of Yahweh” of which both Amos and Isaiah speak, each in his own historical setting, thus refers to the immediate future of the people, which will be radically altered.
The presentations in Zeph 1:7ff. and Ezek 7 (Zimmerli, Ezek, Her m, 1:201f.), where the day of Yahweh is directed exclusively at Israel, are more extensive; following the catastrophe of 587 (in Ezek 13:5; 34:12; Lam 1:12; 2:1, 21f., characterized retrospectively as “Yahweh’s day,” etc.), the judgment of Yahweh is predominantly but not exclusively (cf. Joel 1:15; 2:1, 11; Zech 14:1; Mal 3:23) directed at the foreign nations (esp. at Babylon in Isa 13:6, 9; at Egypt, Ezek 30:3; at Edom, Obad 15; cf. further Isa 34:8; 61:2; Jer 46:10; Joel 3:4; 4:14). The transferal of the concept from judgment prophecy to salvation prophecy and vice versa is facilitated by the essentially ambivalent nature of the day of Yahweh; it brings judgment upon the enemies of Yahweh and salvation for his people. The deciding factor depends upon the side to which Israel or the addressees belong. The concept of the day of Yahweh thus constitutes an essential point of contact between the prophetic proclamation of judgment and of salvation and demonstrates their inner unity (cf. TLOT, p. 539).
In a sense the exile marked a turning point. Now – in Lam. 1:12; 2:1, 21f., for example – people look back upon the “day of the wrath of Yahweh.” With the fall of Jerusalem and the temple, the “day” has already come and the prediction has been fulfilled (cf. Ob. 8; Ps. 137:7). But the “history” of the “day of Yahweh” has not thereby come to an end. Obadiah declared: “For the Day of Yahweh is near for all the nations” (cf. Ob. 15a NJB).
In postexilic prophecy, the formation of the didactic tradition continues. The “day of Yahweh” gradually becomes the nucleus around which crystallizes a complex eschatological drama, as we see above all in Joel 1-4(1-3) and Zech. 12-14. As will be seen, the former has been partially fulfilled. Only the latter, in its entirety, must still take place. The “day of Yahweh” can bring both disaster and deliverance; it can come to both Israel and the “nations”. The final stage is the apocalypticism of Daniel, where yôm yhwh “day of Yahweh” is replaced by qe?, “end”, and other fixed terminology.
Later, through the prophet Malachi, another “great and fear-inspiring day of Jehovah” was foretold. At Pentecost of 33 CE Peter explained that they were experiencing the fulfillment of Joel’s prophecy (2:28-32) concerning the outpouring of God’s spirit, and this too was due to happen before the “great and fear-inspiring day of Jehovah” (Acts 2:16-21). That “day” came in 70 CE when Jehovah caused the armies of Rome to execute divine judgment upon the nation that had rejected His Son (cf. John 19:15; Dan. 9:24-27).
Although with the passage of time the eventful nature of the “day of Yahweh” came increasingly to be emphasized, along with other attributes, its temporal nature was still preserved. This is shown by the various words for time that cluster about the “day of Yahweh”. The divinely inaugurated period of time is denoted by “there are days coming” (Am. 4:2; 8:11; 9:13; Jer. 7:32; 9:24; 16:14; 19:6; 23:5, 7; 31:27, 31, 38; 33:14; 48:12; 51:47, 52), or “in those days” (Jer. 3:16, 18; 5:18; 31:29; 33:15f.; 50:4, 20; Ez. 38:17; Jl. 3:2; 4:1; Zech. 8:6, 23), or “at that time” (Amos 15:13; Is. 18:17; Mic. 3:4; Zeph. 1:12; 3:19f.; Jer. 3:17; 4:11; 8:1; 31:1; Ezek. 7:7, 12; Dan. 12:1).
In the LXX, yôm is almost always rendered by heméra, which emphasizes the chronological character of the word. Here it acquires the meaning “time” more pronouncedly than elsewhere in Gk . under the influence of OT usage. There is, however, a return to pre-Christian thinking in the use of heméra theou, and also of heméra kuriou with reference to God, in non-Pauline literature, although here, too, we may discern a similar and materially perhaps even stronger influence of the Jewish apocalyptic. In 2 Pet. 3:12, as in Jewish conceptions, the heméra theou, which is an alternative for heméra kuriou in v . 10, is the time of the cosmic conflagration (cf. Sib., 3, 54) [Sibyllines, the Sibylline Oracles in 14 books, collected in the 5th or 6th century a.d. for the propagation of Judaism or Christianity, composed at various periods, and predominantly Jewish but partly Christian in derivation.] It may also be the time of the war of the true Ruler of the world against the kings of the earth (Rev. 16:14: heméra hei megalei tou theou; cf. Ac. 2:20, quoting Jl. 3:4). The absolute use of heméra (without genitival attribute) is used for the day of judgment at 1 Thes. 5:5; 1 Cor. 3:13 and Hebr. 10:25. This is to be explained in terms of OT terminology.
The Qumran literature uses yôm without significant change from OT usage. On the further history of the concept of the “day of Yahweh” with new terminology (“day of God,” “day of the Lord,” etc.) in early Judaism and in the NT, cf. e.g., P. Volz, Die Eschatologie der jüdischen Gemeinde im ntl. Zeitalter (1934), 163–65 (cf. Mal. 3:19: ??????? ). See also TDNT, vol. II, pp. 945-947, 951- 953; TDOT, vol. VI, p. 19, 28-32; TLOT, pp. 537-539.
Summary : The future expression yôm yhwh “the day of Jehovah” therefore starts with the great tribulation (cf. Dan. 12:1; Joel 2:2; Matt. 24:21, 22) and ends with Armageddon (cf. Zech. 14:1-7; Rev. 16:14, 16).
Christ’s day
The heméra kuriou of 1 Thes. 5:1-5 points to Jehovah’s day. Mention is made of a “thief”, as well as “sudden destruction”. This reminds one of 2 Pet. 3:10 and Rev. 16:15.
In Luk. 17:24, however, Jesus describes the day of the Son of Man when He shall appear in the glory of the kingdom. Instead of the “day of the Elect” of Eth. En . 61:5 [Ethiopian Enoch, ed. A. Dillmann, 1851]; R. Charles (1906), here has the “day of the Son of Man” . If this is indeed the case, this implies a mere shift in terminology by Jesus on the basis of the equation of the Son of Man and the Elect in Enoch itself (cf. Nestle, E., Nestle, E., Aland, K., Aland, B., & Universita¨t Mu¨nster. Institut fu¨r Neutestamentliche Textforschung. (1993). Novum Testamentum Graece (27. Aufl., rev.) Stuttgart: Deutsche Bibelstiftung). In Jn. 8:56, too, His day is the day of the definitive revelation of His glory (cf. 4 Esr. 13:52, which is perhaps post-Christian).
In Paul, on the other hand, the “day” plays an essential part as the day of world judgment for the community (1 Cor. 1:8; Phil. 1:6, 10 [1 Cor. 5:5?]), for the apostle himself (2 Cor. 1:14; Phil. 2:16) and also, of course, for non-Christians. [It is hard to understand why Kabisch, 266 sees an equation of the “day” and the millennium in Paul. Certainly no passage gives grounds for the assumption that Paul understood the day of judgment as also “day as the time of light in antithesis to night” (Kabisch, 236).] In the passages above its main importance is as an ethical incentive.
In 2 Thes. 2:1, 2 the primary concern is the parousia of Christ and therefore the definitive manifestation of his glory. Obviously in Paul, as in the Gospels, and Revelation, Christ is the Lord of this ?μ?ρα . It is true that in Thes. we find only heméra kuriou, but in 1 and 2 Cor. this is sometimes enlarged to heméra tou kuriou heimen Ieisou, while in Phil. we have the simpler heméra Xristou [ Ieisou ] (cf. TDNT, vol. II, pp. 951, 952).
Finally, in Rev. 1:10a we discover the phrase en tei kuriakei heméra “in the Lord’s day”. Contrary to common opinion, this phrase does not refer to the “day of Jehovah”, i.e., Judgement Day. The context points to Jesus Christ as the Lord whose “day” this is. Immediately after coming “in the Lord’s day,” John heard, not the voice of Almighty God, but that of His resurrected Son (cf. Rev. 1:10-18). This day would be closely connected to Christ’s parousia (cf. 2 Thes. 2:1, 2).
Summary : “Christ’s day” begins with his coronation (cf. Ezek. 21:25-27; Dan. 4:17, 25; 7:13, 14), and ends with him handing back the kingdom to his Father. This is to occur after the Millennium (cf. 1 Cor. 15:24-26; Rev. 6:1, 2; 20:7-10).
