Hi Lyle,
 
You can be sure that when Scripture says there will be 1,260 days that's exactly how many there will be, and when it says there will be 1,290 days it also will be exactly so. The 30 day difference between 1,260 days and 1,290 days can be accounted for. God created  the same number of days in seven 'Hebrew years' as there are in seven 'solar years'. That would be 2,550 days which is 85 Hebrew months of 30 days each. ie. 30 x 85 = 2,550  ie. 1,260 + 1,290 = 2,550 or 364.25 days X 7 = 2,550 days. The Hebrew Calendar adds one extra month every seven years ie. Adar I and Adar II to cpmpensate for the 30-day Hebrew month over seven years.
 Is it not possible that God's plan is that exactly 30 days after the abomination is set up at 1,290 days before the end of the great tribulation that the five 1,260 day Scriptures you quoted will begin therefore fulfilling all the Scriptural requirements to the exact day-count?
 
Merry Christmas to all.
 
YBIC, Bruce Warner