The only decent option is Get Panties, which is well over 10 mins long. I guess there could be a lipstick category? Otherwise it's just Spike% which is... not the most compelling category
Many parts of the game are effectively self-contained levels (e.g. Egg Corridor, Grasstown, and of course the whole lead-up to Ballos), so those could be potential level categories. That being said, I've only been following this game recently, so I wouldn't be surprised if this has been suggested before.
+1 for time attack challenges. All of them should take under 10 minutes to complete quickly, and are tracked on a separate leaderboard (https://www.speedrun.com/cave_story_time_attack_challenges).
If you don't have a copy of Cave Story+ or would prefer to play on freeware there's also a Freeware Hell category there which you could run.
