There are only hours/minutes selectors, so even if I made something wrong the cron should be executed within the first day.
I’ve seen your post and I was going to answer right now.
It seemed to be A BIT faster at some moments, but a few hours ago I experienced the “3900 users are already loggen in, sorry” error again.
Anyway, talking with a friend who uses profreehost.com (which I think uses iFastNet too for the similar Panel graphics) he said that that site has had this same problem for an year, and it seems that they can’t solve it.
So I fear that the problem could be more serious than expected.