This game is the closest to best execution of a tower defense game in this jam, and while I really liked it's good mechanics and challenging levels, I had one very big problem, which is the timer
I really don't understand why you went with a timer instead of a spawn limit, it would add so much depth to the gameplay that it was missing
The problem with the timer is that you're essentially making the player spam left click to spawn tons of enemies, and only target once in a while to make sure the enemies hit the right tower. and it's even worse when the other mechanic is the respawning of the towers
The reason I think it has so much potential is because targeting towers and spawning enemies are good mechanics, and a great take on the jam's theme, just turn it into a strategy puzzle game rather than a slightly strategic clicker game
Please don't take this feedback as discouraging, because I'll still rate the game high, I'm just judging your idea from a developer's point of view
TLDR: the game was fun, with a lot of potential, well done!