I wouldn't worry about it too much. I find myself up at 4 am some mornings working, putting together emails, especially if it's something exciting or on my min

I wouldn't worry about it too much. I find myself up at 4 am some mornings working, putting together emails, especially if it's something exciting or on my mind. If he only requires 6 hours of sleep he might be turning in at 10pm and up at 4am. Or sometimes I find myself up for an hour or two around 3 or 4 am and then go back to bed after clearing my mind, finishing up some code, sending some emails, making notes about an idea. So I wouldn't worry too much about when he's up emailing thinking about his business. But you definitely are only productive 8-12 hours per day tops, maybe less. But being excited about something can result in getting an early start or being up an hour or two in the middle of the night. If you notice he's exhausted, making lots of mistakes then think about asking him if he's getting enough sleep or wants to take the afternoon off.