I came up with that idea because I wanted to run a category which contains all levels of the game, but with real times of 6h+ All Teensies and 100% are too long for me at the moment.

To run NG+ All Levels you would start with a 100% save file (like the one linked in the Resources page), and complete all levels in any given order without additional restrictions. So I would suggest the timing starts after the loading screen of the first level you enter, and the timing ends at the end of the last level you will complete (depending on your oder of the level after the last hit on a boss, entering the exit door on a normal level, reaching the end of a invaded level or music level).

someone probably needs to run it first

I did a run of it just for fun before without practicing before :D But it is the only run I did of it so far. https://www.youtube.com/playlist?list=PLaSZq93-qwKFP0WdZuMHxwWlFXLGr36Oc

I have an another idea of category : the 2 players wii u with a normal and a murphy player on the gamepad

But I can publish any video because I can't capture on wii u...