The bible clearly states that Satan has 1260 days, so the great tribulation can not last more than 1260 days.  Jesus said in Matt 24 that once you see the abomination of desolation then you should head for the hills because then after this time the great trib is going to start.  There has been no abom of desolation so the great trib has not started.
The bible never states that the 2 witnesses are for 1260 days before the great tribulation.  They just have to start at least 3.5 days before satan is cast down.  Jewish people have always believed Elijah (one of the 2 witnesses)is coming back on passover.
 
I believe Ron is 100% correct about Satan being cast down April 11, 2012 and about Jesus returning on Sept 14, 2015 leading up to the final battle of Armageddon on Sept 23, 2015.  I do disagree on the rapture with Ron although he has some great points.
 
I do believe with Ron the 70th week started in 2008 but I believe it started Sept 29, 2008, hence the 1290 days to the abomination of desolation from Dan 12:11.  You could say we have been in a time of tribulation but not the great tribulation.
 
I posted recently why the 2 witnesses should show up on the night of passover April 5, 2012.
I will eventually post why Jerusalem will be divided (or something significant to its division) on Feb 6, 2011
Will Schumacher