What is the ratio between real time and in-game time?

If I set something to happen in “2h”, it means it will happen in 2 hours in-game. But how long it is in milliseconds or real time? There are many things in the game that are measured in milliseconds, and I need to synchronize two times, each using one different type of unit…

There are some functions in the server service stonehearth.calendar, like realtime_to_game_seconds(...) and debug_game_seconds_to_realtime(...).