We all have our favorite characters, so it makes sense that we’d rather take certain members of SEES to Tartarus with us than others. Unfortunately, this means you’ll have under-level members in your party, which is what makes the Great Clock such an important addition to Persona 3 Reload.

The Great Clock can spawn after you reach the 70th floor. You can get a tutorial for it starting at the 71st floor. To summon the Great Clock, you can do one of two things:

After that, Fuuka will let you know that a door has appeared on the floor. Go through it to gain access to the Great Clock. The Great Clock appears randomly and only once per Dark Hour.

If you want a higher chance of it appearing, just unlock chests as you come across them. They don't have to be chests from Floor 71 and above. Also, I really think you should only heal your party when you really need to. Seven Fragments is a lot.