I know how it is to be a game dev on a deadline and have ideas of how to expand on a project, how it can be fixed or added to, etc. So please understand if I mention things you already want to fix or add.
1) Your general platforming feels solid. There isn't a lot of skidding when changing direction of movement, you slow down slightly when sliding down walls, and the game checks for inputs when you're about to touch the ground. The limited number of walljumps is a system that's easy to understand after a few goes experimenting with it, maybe not very well conveyed upfront though.
1a) Walljumping by holding the direction the wall is in works fine. Walljumping doesn't work if you're standing alongside the wall, and it doesn't work if you press jump in tandem with holding the opposite direction - so if you try to walljump away from the wall, you end up falling uselessly downward. You have to walljump towards the wall, and then veer back, which can eat away the momentum you need to reach the opposite wall in time. Since there is an input buffer for checking the jump button before touching the floor, there should be a similar buffer when the player is not overlapping a platform/wall, where the player isn't affected by gravity for a few frames, while the game looks for jumping inputs. It would be ideal to have the game detect if the player is pressing jump while they're mid-air up against a wall, and have them automatically jump in the opposite direction, the same result as the player holding the opposite direction from the wall while trying to walljump
1b) Also, I really feel that walljump count should be bumped up to 4 at the very least. Either that or those walljump-restoring gems should respawn in place after a short time. Because of everything mentioned above, it's very finicky doing challenges that use up all the walljumps, even with the gems restoring them
1c) A more forgiving hitbox would be much appreciated, especially on the castle parapets-themed level with spikes lining all the walls. Checkpoints would also be much appreciated. Though, I feel like these are things you wanted to implemented but didn't have time before the deadline
2) The intro level (the hub??) doesn't seem to follow the same rules as the levels do when it comes to the music acting as a timer, so the first level restarting after a quick audio fade-out almost seemed like a bug at first. It caught me off-guard, anyway. It's difficult because I want to suggest something like 'a text prompt explaining the mechanic' but that betrays the point of using the audio, which is to NOT rely on text to convey the timer. Having a game with no HUD can be an artistic choice that pays off if everything is still reworked to be clearly understood. At the very least, I'd like if it the music faded in a little at the beginning when the timer resets the level. It's a sudden audio jump that doesn't really help the presentation
4) As I mentioned above, I do like the audio mechanic! That and the general lack of UI clutter give the game an interesting experience to get immersed into. Since the game would have to lack an options menu, save-file screens etc to keep up the aesthetic, maybe it would be better for a Deluxe version to have a separate .exe for handling saves and resolution/sound settings, control settings and the like
Currently the game feels like it belongs in the 'rage' subgenre of platformers, which really contrasts against the audiovisual presentation. Maybe that's an intentional contrast you can capitalise on? Regardless, it's a good start for a platformer but it really needs to shine and stand out more in some form of fashion. Look at what we have at the moment (narrative, mechanics, level design, etc) and see what can be changed to make it more outstanding, since things like "good graphics" or "good story" or "a levelling system/skill tree" aren't really unique selling points - hundreds of games have them. What makes your game (potentially) one of a kind? What can be iterated upon? Whether that's really working on the UI-less presentation, or finding more ways to integrate audio mechanics