If you're just worried about putting a high number of hours into the game, I don't see where that's a problem. Everyone has a different situation and set of responsibilities so if you have that many free hours and are sitting around bored, do whatever to keep yourself entertained. If you still feel bad about it you could divide that time up with another hobby or two on top of ffxiv.

If you're worried because you find yourself skipping out on family or friends to play the game, procrastinating on chores/errands, or prioritizing the cash shop or other extras over a need, that's when it becomes a problem. If it's putting you in uncomfortable situations because you spent time playing that should have specifically been spent elsewhere.

I spend about 15 to 20 hours, sometimes more if there's something in game that I'm really excited about, less if I'm busy or can't make it online for some reason. Just went through a bad storm so haven't been online yet this week.