Thanks for checking out my game and leaving feedback!
I like your idea with giving a warning when the time is about to run out - I'll implement something to that effect in a post-jam build. Maybe some kind of a sound clue or a countdown on top of the player ship will do the trick. It's definitely too hard to keep track of the time left in the heat of battle currently.
The crazy difficulty was not entirely intentional on my part: during the development I tested the mechanics with several pre-placed enemies and everything seemed okay. And then, as submission deadline approached, I placed some more enemies, added an automatic enemy spawner and ran out of time for playtesting. ¯\_(ツ)_/¯