Correct, General Caster has a slightly different language/format so you will need to adjust your formula, you can’t just insert the same Monday formula.
You may want to reach out to @rob from General Caster for help as I’m not sure how Monday stores the data from Time Tracking. I was able to output some info via General Caster but it doesn’t seem like its showing the minutes(only the hours). May just require some format tweaking though. Check this post for GC, someone may have already asked your question.
I completely understand your frustration with the formula column not being supported by automations but if you’ve seen on the many other post/request, it’s a issue that requires Monday to completely restructure how the formulas work. Currently they are stored on the client side, not the server side which means not many work arounds exist either because of that.