It looks like there's still an issue with this - I'm working on it.
I'm fixing this in the next release, and improving the way it works. You will now be able to refresh every 2 (closest to real time...), 5, 10, 20, 30 or 60 minutes and it will show a countdown timer to the next update (and refreshes will continue indefinitely, until you cancel it). You will be able to toggle up/down in the list of options by using the left/right click.
If I'm reading between the lines, what you would really like is the full power of the Code Mirror editor :)
Google's way of exiting preview is either going back to the GTM Container and doing "Leave Preview Mode" or when using a shared preview link, reload that link and click on "Exit preview and debug mode" - both methods aren't very practical... so now you have a nice and handy "Exit Preview" button. It will simulate what the shared link method does and get you out of preview for the current container.
Customer support service by UserEcho