I and a friend, played Reach the whole new year's eve last year.
8PM - 6AM
But, we wouldn't do that again ( at least I wouldn't, because I discovered Black Ops ). My friend will arrive in an hour, so we will pull a 12h again. I'll suggest that we go play Black ops, but he will most likely be against it since he hates it. So we will most likely end up watching movies like Rise of the planet of the apes.