Can you explain why in Revelation the second half of the tribulation is 1260 days and in Daniel, the second half is 1290 days? Somewhere during the last 7 years of Jacobs trouble, there must be a leap year (extra 30 days) added because of the 360-day Jewish calendar. Is that what happens?
There is no contradiction here, only a misunderstanding. In Daniel 12:6 Daniel asked the angel how long it would take to fulfill the things he had been talking about in the previous 5 verses to be fulfilled. The angel answered, “It will be for a time, times and half a time.” This phrase is repeated in Rev. 12:14 and is a euphemism for 3 1/2 years, the length of the Great Tribulation. (A time equals 1 year, times equals 2 years, and half a time equals 1/2 a year.)
Then in Daniel (and only there), the angel gave two other time spans. One is 1290, and the other is 1335 (Daniel 12:11-12). The angel did not explain this, but many scholars believe the 1290 days combines the length of the Great Tribulation with the time required for the judgments of survivors Jesus will conduct after His return (Matt. 24:45-Matt. 25:46). Then an additional 45 days is added to that, which may refer to the time it will take to set up the government, cleanse the Temple, and make final preparations for the Millennial Kingdom to begin, 1335 days after the Abomination of Desolation.