Jeffro, this is how I see it. Note there will be celestial phenomena twice, at the beginning and at the end of the Tribulation. Jesus' Olivet discourse, especially Matthew and Luke, serves as a confirmation of the Revelation chronology (Matt. 24 & 25; Mark 13; Luke 21).
A. Pre-tribulation period. Jesus said: “Nation will rise against nation, and kingdom against kingdom; and there will be great earthquakes, and in one place after another pestilences and food shortages; and there will be fearful sights and from heaven great signs” (Luke 21:10, 11; cf. Matt. 24:6, 7; Rev. 6:1-8). This is a fitting summary of the first phase of Jesus’ composite sign.
B. Prelude to the tribulation. Above prepares the way for the breaking of the sixth seal. Jesus continues: “Also, there will be signs in sun and moon and stars, and on the earth anguish of nations, not knowing the way out because of the roaring of the sea and [its] agitation, while men become faint out of fear and expectation of the things coming upon the inhabited earth; for the powers of the heavens will be shaken” (Luke 21:25, 26; cf. Rev. 6:12-17). This introduces the second phase of his prophetic sign.
C. Great tribulation. As seen, successive cosmic disasters and deadly plagues lie in wait. This is to be the tribulation proper. Jesus warned: “Keep praying that YOUR flight may not occur in wintertime, nor on the sabbath day; for then there will be great tribulation such as has not occurred since the world’s beginning until now, no, nor will occur again. In fact, unless those days were cut short, no flesh would be saved; but on account of the chosen ones those days will be cut short” (Matt. 24:15, 20-22; Mark 13:14, 19, 20; cf. Dan. 12:1; Rev. 8, 9, 11, 15, 16). This describes conditions during the tribulation, the third phase of Jesus’ warning sign.
D. Post-tribulation period. After the Tribulation, during Jesus’ Second Coming, celestial phenomena will again be the order of the day. This is the beginning of the LORD’s Day (Mark 13:24, 25, 28-32; Luke 21:27-33 NIV; cf. Is. 13:9-13; Joel 2:1, 2a; 3:14-16; Rev. 16:14, 16; 17:12-14). This is the fourth phase of his prophecy.
E. Judgment. Jesus will be filling the dual role of judge and
executioner during the period of his Second Coming (Matt. 25:31-46; Acts 17:31;
cf. Rev. 11:18; 14:14-20; 19:11-21).
This is the fifth and final phase of Jesus’ composite sign.