Karaoke runs from 2PM to 2AM this year. I feel like it ended later in previous years?
Certainly, there is plenty to do at night if you are a night owl. Video rooms, gaming, dances, karaoke, etc. Is Stage Zero 24h? Unofficial activities also take place, like room parties, drinking at bars, or even just hanging out in the halls. You'll always see at least a few groups of people at 3AM playing Cards Against Humanity or other games at the large round tables on the Marriott side of the concourse, as well as people sitting on the floor. If you want to stay up, you can easily find something to do.
Though, I recommend getting at least some sleep. :] I haven't been out at the con between around 4~7AM, but between 7~9 or 10AM it's pretty slow, except for things like video rooms. I think most people are sleeping off their late nights at that point. You can always take short naps during the day, too.