Well, assuming the Jewish calendar is correct, and assuming Revelations is correct, a day can be 1000 years, or it can be any amount of time God decides He wants to make it.God didn't make our "day", humans decided what a day was.
Notice that it is the dragon, "Satan, he deceiving (in the present) the whole habitable world", cast down to EARTH. This future event is described as occurring at the mid-point, day 1260 of Daniel's 70th Week, with 1260 days remaining of the tribulation.
So if the Tribulation occurs in the 70th week of Daniel, how many years in a week?