I think of a standard contra dance as running 8pm-11pm: three hours is a nice amount of time for dancing, and 8pm is late enough that dinner isn't rushed. Looking over the 136 regular Free Raisins dances from 2010 to 2019 matches my impression: 85% were 3hr, 62% started at 8pm, and 51% did both.
I think this is out of date, however, and dances now tend to be earlier, shorter, or both. For example, in the Boston area the regular dances are:
And, as of this Sunday, BIDA now additionally has a 4:30-7:30 dance on 4th Sundays.
Similarly, while I don't have times written down for Kingfisher gigs the way I do for Free Raisins ones, when I look over the last twenty regular gigs we've played I see eleven (55%) are 2.5hr or shorter, and fifteen (75%) started at 7:30 or earlier. Only one (the excellent Flying Shoes dance of Belfast ME) was 8-11.
I don't know what things looked like before I was old enough to notice, but I did find a bit of history from Boston's Thursday dance:
On a cold Thursday night in February of 1978, dancers, Rod and Randy Miller, and Tod Whittemore were waiting in the lobby at the Cambridge YWCA for the aerobics class to end. At the stroke of 9pm we rushed into the hall to set up the sound equipment and tune up, while the dancers changed out of their winter clothes. At 9:10 the first Thursday Night Dance began.
I don't think any dances start that late today, though it's also possible that 9:10 was something temporary due to difficulty finding a spot that was available at the right time?
Overall, I prefer the earlier times, which are easier for me both as a parent and musician. I'm excited about bringing my kids to the new 4:30-7:30 BIDA dances, and dances that end sooner are easier to drive a long way home after. I'm less excited about the shorter dances: it means the effort of getting to and from the dance, setting up the hall, etc is amortized over less time dancing, and it makes the overall evening feel compressed. On the other hand, I do think shorter dances can be the best of a few bad options when handling declining attendance: it's not a great experience trying to keep a dance fun when it's 10:45 and you're having trouble scraping together enough people for a triplet.