I don't subscibe to the '1 hour before midnight's worth 2 after' business, but I do think that different people have different times of the night when they can miss sleep without it bothering them and , contrarily, times when missing a couple of hours really mucks up their next day. For me it is the hours between about 4am and 6 am that really affect me. If I don't sleep then I'm dreadfully tired. Doesn't seem to matter too much if I'm awake before then.