I worked as a server for years first but when I first got into tri it was hard but it wasn’t long before I could manage 20hrs/week while serving 7x a week. I took a 4 month break while visiting my GF out of country and expected to be able to train 30hrs/week no problem when in reality I could only add 2ish hrs with the same fatigue to the work offered very little limitation as it turns out for me.

Edit: should add that while i was working 7days/week my shifts were 6-8hrs but still logged 10-15km per shift. I had zero live outside work/tri but made 8+hrs sleep a priority.