Interesting idea! I like that time is simultaneously a score, currency, and health all at once :)
I must say, a fan of the enemy designs, they look really trippy :D
I don't really know what I'm doing, but I managed to pass to endless mode with 30 minutes remaining, I think part of that is the ability to start like 3 waves at once :]
But otherwise very cool, impressive that you made a whole tower defence game with multiple towers, upgrades, targeting priorities, and interesting enemies :D