Bear in mind that Daniel is quite clear that the "Abomination of Desolation" is the heathen altar that stood in the Temple during the reign of Antiochus IV Epiphanes who profaned the Temple and persecuted the Jews for 3 1/2 years (i.e. from 167-163 BC). Chapter 11 makes the identity of the king quite clear (describing his career and those of his predecessors in exquisite detail), and it does violence to the original conception of the narrative to apply some aspects of it to a completely different time and historical context. The actions of this king over the 3 1/2 year period are described in a series of visions:
"He is going to speak words against the Most High and harass the saints of the Most High. He will consider changing seasons and the Law, and the saints will be put into his power for a time, two times, and half a time. But a court will be held and his power will be stripped from him, consumed, and utterly destroyed" (Daniel 7:24-26).
"It challenged the power of that army's Prince; it abolished the perpetual sacrifice and overthrew the foundation of the sanctuary, and the army too; it put iniquity on the sacrifice and flung truth to the ground; the horn was active and successful....How long is this vision to be -- of perpetual sacrifice, disastrous iniquity, of sanctuary and army trampled underfoot? ... Until two thousand three hundred evenings and mornings have gone by, then the sanctuary will have its rights restored" (Daniel 8:11-14).
"After the sixty-two weeks, the anointed one will be cut off (= the assassination of the high priest Onias III in 170 BC) with no one to help him. The forces of a ruler who is to come will destroy the city and sanctuary. His end will be in a cataclysm and unto the end of the decreed war there will be desolations. He will make a strong alliance with the multitude for one week (i.e. the 70th week, from 170-163 BC). For half the week he will suppress sacrifice and offering (i.e. from 167 to 163 BC), and the abomination of desolation will be in their place, until the predetermined destruction is poured out on the desolator" (Daniel 9:26-27).
"Forces of his will come and profane the sanctuary citadel; they will abolish the perpetual sacrifice and install the abomination of desolation there. Those who break the covenant he will corrupt by his flatteries, but the people who know their God will stand firm and take action. Those of the people who are learned will instruct many; for some days however they will be brought down by sword and flame, by captivity and by plundering" (Daniel 11:31-33).
"From the moment that the perpetual sacrifice is abolished and the abomination of desolation erected: one thousand two hundred and ninety days. Blessed is he who stands firm and attains a thousand three hundred and thirty-five days. But you, go away, and rest; and you will rise for your share at the end of time" (Daniel 12:11-12).
This king is thus said to (1) abolish the perpetual sacrifice in the Temple, (2) change the Law and seasons (= seasonal festivals), (3) wage war against Jerusalem and desolate the city, (4) persecute those faithful to the covenant, (4) make a pact with those willing to break the covenant and flatter them, and (5) install an "abomination of desolation" (in the Aramaic, the sense is more "an appalling horror"). This would occur for a literal but varying period of 3 1/2 years (depending on which events one chooses to start and end the period with), as indicated in ch. 8 which refers to 2,300 half-days (=1,150 days of cessation of DAILY sacrifice, given in the morning and evening in the Temple) and ch. 9 which refers of a "half-week" of suppression of sacrifice and of profanation of the sanctuary by the "abomination of desolation" (in which 1 week = 7 literal years). The detailed prelude to the reign of Antiochus Epiphanes in 11:2-20, describing the flow of history from 336-175 BC, fixes to identity of this "wretch" as Antiochus. The historical account in 1 Maccabees (written in the late second century BC) describes exactly the actions narrated in Daniel and identifies the "abomination of desolation" as the altar erected by Antiochus:
"Once Antiochus had his authority established, he determined to make himself king of Egypt and the ruler of both kingdoms. He invaded Egypt in massive strength (= Daniel 11:25), with chariots and elephants and a great fleet. He engaged Ptolemy, king of Egypt, in battle and Ptolemy turned back and fled before his absence, leaving many casualties....After his conquest of Eygpt, in the year one hundred and forty-three, Antiochus turned about and advanced on Israel and Jerusalem in massive strength. Insolently breaking into the sanctuary, he removed the golden altar and the lamp-stand for the light with all its fittings, together with the table for the loaves of offering, the libation vessels, the cups, the golden censers, the veil, the crowns, and the golden decorations on the front of the Temple, which he stripped of everything. He made off with the silver and gold and precious vessels, he discovered the secret treasures and seized them, and removing all of these, he went back to his own country, leaving the place a shambles and uttering words of extreme arrogance....The days passed, and after two years the king sent the mysarch through the cities of Judah. He came to Jerusalem with an impressive force, and addressing them with what appeared to be peaceful words, he gained their confidence; then suddenly he fell on the city dealing it a terrible blow, and destroying many of the people of Israel. He pillaged the city and set it on fire, tore down its houses and encircling wall, took the women and children captive....They shed innocent blood all round the sanctuary and defiled the sanctuary itself....Her sanctuary became as deserted as a wilderness, her feasts were turned into mourning, her sabbaths into a mockery....Then the king issued a proclamation to his whole kingdom that all were to become a single people, each renouncing his particular customs. All the pagans conformed to the king's decree, and many Israelites chose to accept his religion, sacrificing to idols and profaning the sabbath. The king also sent instructions by messenger to Jerusalem and the towns of Judah directing them to adopt customs foreign to the country, banning holocausts, sacrifices and libations from the sanctuary, profaning sabbaths and feasts, defiling the sanctuary and the sacred ministers, building altars, precincts and shrines for idols, sacrificing pigs and unclean beasts, leaving their sons uncircumcised, and prostituting themselves to all kinds of impurity and abomination, so that they should forget the Law and revoke all observance of it. Anyone not obeying the king's command was put to death....On the fifteenth day of Chislev in the year one hundred and forty-five (= 8 December 167 BC) the king erected the abomination of desolation above the altar; and altars were built in the surrounding towns of Judah and incense offered at the doors of houses and in the streets. Any books of the Law that came to light were torn up and burned. Whenever anyone was discovered possessing a copy of the covenant or practicing the Law, the king's decree sentenced him to death. On the twenty-fifth day of the month sacrifice was offered on the altar erected over the altar of holocaust. Women who had their children circumcised were put to death according to the edict with their babies hung around their necks, and the members of their household and those who had performed the circumcision were executed with them" (1 Maccabees 1:16-61).
The interpretation of the "abomination of desolation" being the Al-Aqsa mosque ignores and distorts many aspects of the visions of Daniel. The days in Daniel are not "years" but clearly literal days referring to the period during which daily sacrifice was abolished. Thus the period of 1,290 days is roughly equivalent to the 3 1/2 times of ch. 7, the 2,300 half-days of ch. 8, and the "half-week" of ch. 9 (if a day equals a year, then the seventy weeks of years would amount to about 179,000 years!). The lengths differ because the persecution, the desolation of Jerusalem, the profanation of the Temple by the abomination of desolation, and the cessation of sacrifice began at different times. The time-period, moreover, pertains to the abolition of perpetual sacrifice in ch. 8, 9, 12 (and ch. 11 also refers to the abomination of desolation as installed during the time of sacrifice being abolished), but the practice of daily sacrifice had ceased centuries before AD 691 (in AD 70, to be precise) and ch. 11 dates this cessation as occuring during the reign of Antiochus Epiphanes. Such a reading does not take in account the literary and historical context of Daniel.