This optional field specifies the amount of online time (in seconds) the user has left. Each time the user logs out, the time they have used is subtracted from the time they have left. If they try to log in and there is no time left, they will not be permitted to log in at all. Each time they log in, their maximum session time will be set to the amount of time they have left, so they should not be able to overrun their time left. See Entering time intervals

If you leave this field blank, there are no limits placed on their online time.