During at least one critical hour of the attack, we can place him: He and Biden were on the phone with Netanyahu. Immediately after, we have photos of Biden, Obama and some of his gargoyles, so we can time it pretty closely.
Check out theconservativetreehouse.com, the timeline there is excellent.
Obama had a fundraiser the next day and a flight to make. He was sound asleep therefore, and didn’t want to be disturbed, IMO.