It's possible to pause marathon mode In-Game Time by pausing the game between levels

Marathon Mode's in-game timing option allows the timer to pause between levels, making the mode more fair to everyone by excluding possible loading times and everything that happens after level completion.

However. This can be exploited by pausing the game after reaching the score screen before loading a level, keeping the game paused without any time penalty. This leaves a grey area where you have to decide if abusing that glitch can be allowed or not. Longer breaks are definitely against the spirit of the speedrun.

This could be fixed by either making the timer keep running during a menu, no matter what is going on, or forcing the next level to load despite being in a menu. The latter option was more popular among speedrun moderators, and I would be ready to try and make a merge request for either of them. Posting this here as an issue though, to have some conversation and possibly find another solution.