Auto Log off

I have my computer set up with an auto log off screen that
is driving me crazy. I am not gone for 15 minutes and it
logs me out and I have to re enter my password and then it
brings me to the original screen where I log on again.
I f you can help me set the delay time for longer (about
17 hours!) or help me get rid of it altogether, it would
be very much appreciated.
Tahnks.
Maria