I set this up but I discovered that the minimum billable time for any git action is 1 minutes, meaning that a script that runs for 14 seconds will still get billed for 1 whole minute.
It's still okay for a lot of scenarios but if you want to use it for something more frequent I think the minutes would rack up. It should maybe be more prominent in the explanation (that it's also a billing issue and not just a "inaccurate timing" issue).
Other than that, huge thanks for this since this is really informative and helped me a lot.