When I'm writing, I don't mind too much how long the time is, so long as there is time to work around stuff like exams which can cause problems. I do like the longest amount of time possible, but it rarely causes me to back out of challenges.
I think it would be a good idea to maybe reduce the number of participants. It has been impossible to keep up with the number of fics and art being posted. I've never managed to read everything, and I still regret that.