ah, thanks! I had suspected that going the longer route was the way to do it, but I hadn't realized that the door timer starts when you step on the button, not when you step off. Makes sense.
I assume the blue and purple spheres at the beginning are to demonstrate how they affect time, but that didn't click for me (because I never stopped and looked). The section after the door, with the pusher gun things, worked a lot better at demonstrating that for me (probably because they force you to stop and look at how the sphere is affecting time). Maybe having that be the first challenge in the game could help people understand how the game works a bit earlier.
Anyway, agreed with the other commenters about checkpoints being necessary, especially with the moving platform being so finicky. Much better game once you get to the time mechanic though, it's a super neat idea and makes for really interesting puzzles.