This might sound kinda stupid (it probably is) but I was thinking if a Challenge Stage category could be a thing. Timing could be done by either:
1. Measuring RTA from entering the first door of the first stage to entering the last door of the last stage, or
2. Adding up the IGTs of every stage

P.S. I'm sorry if this question has already been raised before.

This is already a part of the 100% run. Also you don't need a leaderboard to run something.

Maybe make it a IL Category

https://cyberscore.me.uk/game/981