They traded half an hour on the (major stages) curfew for a few decibels in the late 00s, yes. They also used to have much shorter changeovers, and now schedule in a 15 minute buffer at the end in case acts overrun. - it used to be pretty normal for subs to start at about 9pm, so starting in the daylight and finishing in the dark, but the combined effect of all those changes means that they're now usually starting a full hour or more earlier than they used to and finishing whilst it's still daylight.