Many options are explored in this thread:
There is one more I just found, in that there is a Timestamp expression in the Geolocation object that gives you UNIX Time based on your system time. While your game is running, save this to a variable/localstorage, then on start, you can get the UNIX Time and compare what the difference is from your saved value to make adjustments accordingly. Haven't experimented with it yet though, it seems like there may be some delay issues when requesting geolocation. The methods in the linked post should be more certain.