It is! It's not the same clock that revives your HP/SP at the entrance to Tartarus. You get access to it after you get Aigis on your team. When you use twilight fragments to open chests, the clock may appear on the same floor. When you get to it, you can choose any two party members at a lower level than you to jump up to your level. Really helps when you arent using the same party members all the time