Nothingness:
if vacations are not allowed, I think it will not encourage me and a lot of players, because you can easily have any incovenience that prevents you from connecting to the site (sickness, holiday, work, connection breakdown,....).
It would be better to have a short time per move. Usually players can be very slow because they have hundreds of games running and they simply play the first one in the time list. They are always near the time limit.
The problem is: what is a short time for you?
For me it is 2 days, with vacation on.
Maybe it is too long for many others.