Which your goal?

on my website , after few minutes of pause , the session is ended and i have this message : "You may experience problems saving content. Please refresh this page.   " 

So when i refresh i return to homePage (Session Destroyed)!  i wan to extend the timeout to some hours or even desactivate this timeout , so session can't be ended until user click on " DISCONNECT "

This is issue due to validateActionToken function:

Validate an action token.
Calls to actions will automatically validate tokens. If tokens are not present or invalid, the action will be denied and the user will be redirected.

I don't think that you need to extend the sessions timeout.

RvR is correct. Do not attempt to extend the timeout. Instead try to find out why the action tokens are not getting renewed like they should.