Hmm, thought there was a thread about the new access/restriction system, but I can't seem to find it.. (or I just might be too tired).. But, basically it works like this:
ulx groupallow <group> <command> "<restrictions>"
For example, if I wanted to make it so admins could slap only themselves with 10-20 damage, you would do this:
ulx groupallow admins "ulx slap" "^ 10~20"
In this case, the <restriction> part splits each argument in the command-- Player, then damage, seperated by a space. Check
this thread for info about how the player part works.
For your case, You would limit ban times like so:
ulx groupallow admins "ulx ban" "* 1~60"
This will make it so admins can ban anyone ("*") for anywhere from 1 to 60 minutes. (Disables permabanning, too, as 0 minutes is outside that range)