7:30 is for Ghost. Maiden has been starting at about 8:50.
A lot of people were talking about it, and in the intermission between Ghost and Maiden I went out to grab a drink and the clerk I talked to told me he had heard it was because Bruce had requested the AC be turned off. I remained skeptical that was the true reasoning but then a local radio DJ said the same thing this morning.
Lots of people around me left throughout the concert to "go and get some air." Was quite unusual, I can't imagine what the difference would have been having the AC on or off for the band members running around on stage.
AC dries out the vocal cords quite a bit, it's actually far better to sing in heat and humidity. Turning off the AC for a whole arena is a lit bit dickish, though. Can't imagine the other band members loved it either.