Four hours is far too short. I want it to at least last 8 hours so I don’t need to log in twice in a typical work day.
Ideally the timeout period would be configurable to whatever the user wants.
I would probably set it to 7 days, personally. But right now I’m stuck with either 4 hours (way too short), restart browser (which I do relatively frequently, as I run Firefox betas and they update a lot), or never, which permanently stores my key and is insecure.