Hi Jonathan, the autologin function should work out of the box for hybrid apps. I tested this feature this week, but I didn't get it working properly on iOS.
Your session length option is not a way to go. You can check the com.mendix.webui.HybridAppLoginTimeOut in custom settings, but the default is -1 meaning no timeout.
Anyways what are your findings? Did you test on iOS or Android?