When you move past the "Start/Clear"pad to start the timer, you span jumps and jump back up to the pad, stopping the timer.

Can this be used in the fastest marathon category, or do you have to go through the marathon normally?

No glitches are allowed in the fastest marathon.. I once got a 1.3s time because of a glitch I found. Also, do you have discord? If so, please join the small Goime 500 speedrunning community via the link in the rules

Yes, I do have a Discord. I'll join it right now.

However, this glitch IS allowed in 100% category in case you didn't know

However, this glitch IS allowed in 100% category in case you didn't know