If Jesus died around 3 pm on a Friday, and rose on a Sunday morning ... that's 9 hrs till midnight, 24 hrs till the next midnight, which together is 33 hrs ... so if he rose at around 7am on Sunday, he would have been in the grave exactly 40 hrs.
Unfortunately, I'm not quite sure it works. For once, I haven't seen the Bible using the number 40 in connection with the time between Jesus death and resurrection. Secondly, apparently sunrise in Israel is no later than at 6:40am even in winter (poor young man that fled naked! he must have been freezing if it really was winter). Also, since it sounds that Jesus died just after 3pm, it might mean He would have risen rather slightly after than slightly before 7am...
The gospels all emphasise that it was on the first day around sunrise (probably dependent on whether you're looking at the time when people leave for the tomb, or arrive at the tomb):
toward the dawn of the first day of the week (Matthew)
very early on the first day of the week, when the sun had risen (Mark)
on the first day of the week, at early dawn (Luke)
on the first day of the week ... early, while it was still dark (John)
Maybe, we should be looking for the number 38 instead, which is also an interesting number (John 5:5). Then, Jesus could have risen at around 5am, and passover could have been in a more warmer time of the year.