In Cowabunga Cranked there is a timer that is constantly ticking down and once it reaches zero the game ends. In order to prevent this, zombie kills adds time, however it gets harder each round as the total time decreases.
Timestamps:
Setting up: 0:00 - 6:48
Building LTG: 6:48 - 8:12
First Aether Canister: 8:12 - 11:39
Strauss Counter: 11:39 - 12:46
Second Aether Canister: 12:46 - 16:30
Setting up for boss: 16:30 - 18:09
Boss: 18:09 - 25:22