At a bare minimum, commutable generally means that you can commute to work (primary flight with a backup) the same day you report, and have at least 1, ideally 2+ flights home after release. Of course that is going to be extremely route dependent. Some people have 6 flights across 2-3 airlines that get them to their hub before 10 AM, others only have 2-3 flights a day total so they need much later starts in the day.

I’d say most people would call anything after noon to be front end commutable, and probably after 1700 for back end. The company has a definition when they post “commutability” but I can’t remember what those times are off the top of my head. Most international is departing late in the evening so you’ve got all day to get to work, whereas a 7AM report probably means having to come in the day before and buy a hotel or crashpad.