A period of 3½ years is a recurring theme in end-time Bible prophecy. The Beast that is described in the later chapters of Revelation is to receive power and authority from Satan for a period of 42 months (Revelation 13:5 Revelation 13:5And there was given to him a mouth speaking great things and blasphemies; and power was given to him to continue forty and two months.
American King James Version×). That is the same length of time that gentiles will "tread" Jerusalem underfoot (Revelation 11:2 Revelation 11:2But the court which is without the temple leave out, and measure it not; for it is given to the Gentiles: and the holy city shall they tread under foot forty and two months.
American King James Version×). In Jerusalem, God promises to raise up two prophets to be His witnesses for 1,260 days. God "feeds" or provides for the woman of chapter 12, representing God's chosen people, for 1,260 days (verse 6). We are told she will be "nourished for a time and times and half a time [3½ years], from the presence of the serpent" (Revelation 12:14 Revelation 12:14And to the woman were given two wings of a great eagle, that she might fly into the wilderness, into her place, where she is nourished for a time, and times, and half a time, from the face of the serpent.
American King James Version×).
Daniel referred to a coming deceiver as a pompous "little horn" arising among the 10 horns on the fourth beast, warning that "the saints shall be given into his hand [as martyrs] for a time and times and half a time [3½ years]. But the court shall be seated, and they shall take away his dominion, to consume and destroy it forever" (Daniel 7:25-26 Daniel 7:25-26  And he shall speak great words against the most High, and shall wear out the saints of the most High, and think to change times and laws: and they shall be given into his hand until a time and times and the dividing of time.
 But the judgment shall sit, and they shall take away his dominion, to consume and to destroy it to the end.
American King James Version×).
In another end-time prophecy, Daniel speaks of "the power of the holy people" as being shattered for the same period of time—3½ years (Daniel 12:7 Daniel 12:7And I heard the man clothed in linen, which was on the waters of the river, when he held up his right hand and his left hand to heaven, and swore by him that lives for ever that it shall be for a time, times, and an half; and when he shall have accomplished to scatter the power of the holy people, all these things shall be finished.
American King James Version×). This recurring reference certainly appears to be significant, indicating that a total of 3½ years will elapse from the beginning of Satan's attack on the people of God until God destroys his military and religious system and locks him away at Christ's return.
Regarding the 1,290 days and the 1,335 days referred to in Daniel 12:11-12 Daniel 12:11-12  And from the time that the daily sacrifice shall be taken away, and the abomination that makes desolate set up, there shall be a thousand two hundred and ninety days.
 Blessed is he that waits, and comes to the thousand three hundred and five and thirty days.
American King James Version×, the context doesn't clearly explain these times. Nor do we have clear understanding of them from another part of the Bible. But we can have confidence that those who wait patiently on God through these terrible times will be blessed in God's soon-coming Kingdom.