I often get the question 'hey, I have to login again, why?'. Currently the system will keep you logged in for 8 hours, which is quite long, but logs you out after that. On for example iOS you are logged out every time you switch from the app in web app mode to another app and back.
Time for a fix, and that fix arrived today: remember me on this device. Enable it to stay logged in for 30 days (until manual logout). Of course, this is still a tradeoff from a security perspective. That's why on mobile platforms the checkmark for remember me will be on, and on desktop off automatically. Of course you can manually change this.
Why the difference? Because mobile phones are much more likely to be personal devices than desktop PC's/laptops, and are often more secure (touchid, pincodes, patterns etc). Also, the problem of logging in every time you open the app is more persistent and irritating on mobile.
For implementing the remember me functionality the workflow of this article. It helped me a lot, and is a good read.