If I make the timer stop sooner, I would also make it require 2:26 instead of 2:30. It's balanced to make it a challenge around that extra time before the clock stops.
Endless strategy: 3 shadow dragons, 1 entropy alien, 1 corpse king.
All attack on Dragons, all elasticity on the Corpse king.
Corpse knocks back enemies and tanks everything, Dragons melt enemies.
I don't know why a trained mage decides that it's time to jump and smack enemies with a little wand and therefore suicide... while having a nearly full mana bar. Twice in a row.
If I make the timer stop sooner, I would also make it require 2:26 instead of 2:30. It's balanced to make it a challenge around that extra time before the clock stops.