I think 8-5 is actually 8 hours in the US: federal laws guarantee you an hour lunch break, just as in the UK. Of course, I imagine in a lot of start-ups that's ignored or perhaps doesn't even hold.
Ah, so that probably means he's not actually working 9 solid hours per day. That's better. I admit to doing the same, albeit at different times of the day (10h-19h).