This script does not authenticate with the GitHub API. That means a maximum of 60 requests/hour. More checks means more API requests, and if you do hit rate limits, currently it's just a silent failure.
Idea: Desktop notification saying "hey you ran into rate limits. this script will not function until after [time]. you can either do nothing or add a token [#5]" which is then silenced until the rate limit is supposedly lifted (write a timestamp in script storage for that, GM_setValue etc.)