I don't like 10min timelimit, because maps were designed for 20minutes, and I hate when I just can't get to win with flags, because of awfully short time.
Severs empty out because map is bad, not because of time left. I just like 20min normal limit I'm used to, because I think it was pretty well balanced, not a rush to win nor a "how-long-can-I-play".
But there are maps I wish there was 1min timelimit. Just improve rotation and locate server so everyone has good ping (like superman locating server in US with most players from EU).
I would say that we should keep default to 20, because it was so for very long and maps are made to play in this limit, but everyone can set it as he wants, I've seen 5min and 30min timelimit before. Maybe option would be to have per-map options like timelimit, point limit, elim time etc. that admin can set.