Machines are on all day and night, well in one section. There is 2 sections: the grand hall, which is where the vendors are and about 60-65% of the pinballs are, they close this off at midnight. The other section is a separate room which is open ALL NIGHT! Last year, when they closed off the main room (at midnight) I went to my room, slept for 3 hours and came back down and played pinball until around 8 am, got breakfast and started visiting the seminars.
P.S. Sleep isn't in existence during the expo. Well, you can sleep but you really don't want to. I was dead tired after the expo was over and my body thanked me for finally getting some real sleep, but it was all worth it.