Does he nap? Did his nap time become his main sleep time? If so, I'd try waking him a couple hours earlier than usual (he will be crabby), making his "morning" super-exciting, with lots of bright light and fun activities, then slowing down and doing calming stuff in a dimly-lit room around the time when you can anticipate him going to sleep. I'd keep doing this a little earlier each day, until his circadian rhythm get reset to daytime wakefulness. I suspect you'd have a bad couple of weeks (crabby, difficult child) until he resets his clock. Also, with naps, don't let them go for too long until he's back on a daytime schedule--two hours max.
at 7:50 AM on Jul. 29, 2009