Art person here, i'm glad you liked our game! The cannons are kinda unintuitive, they remove the total amount of sand from the player so they have to jump faster, I believe the player starts with 6 seconds split between the two halves and each shot removes 1 second worth of sand. Sand cap is restored upon entering a checkpoint (perhaps for the first time?) or respawning. To be honest, it would have been better if they dealt knockback but on some levels that was deemed too punishing and we didn't end up implementing it.
Yeah. Programming person here, specifically, the cannons deal 0.8 seconds of damage. Originally, I set them to 1.5 seconds but someone nerfed them and I didn't realize (oh well). Also, yeah, it would've been awesome if they specifically did knockback, but it would've required reworking too much for the time we had left.