10:00 PM, having started at 4:00 AM earlier, with intervals in between for nesseccities, such as the bathroom etc., due to a time difference between Taiwan and the U.S. which left me extremely screwed up sleep-wise. That was like, four years ago though. (I remember this because my friend wouldn't stop calling me until I unplugged the phone)
But more recently, the latest I sleep in is 8:00 or 9:00 AM. o o;