Go to OnPlayerConnect of the script. There look for SetTimer or SetTimerEx and change the 1800000ms (=30 minutes) to whatever you like.
If you cant find it, just search for 1800000 in the script with ctrl+f and change it.
Nevertheless, Benjo is right. Please do not post request without any info about the script you are using. Give at least its name, or better the relevant code part of it.