IRAT reselection priority criteria

Hi all,
I’ m facing with a doubt.
Related to RAT priority, there is some irat reselection timer that manage it?
For example, if I power on a device or i’ m in a RAT that is not high priority, there is a timer that regulates it?if I’m in gsm…there is a timer that allows me to stay in gsm, and if it expires, I have to search for a higher priority rat?
Thanks a lot