There is actually a soft limit on how long you can play, with a “you win!” at 300 seconds, and you shouldn’t be able to play much longer anyway because the black cancerous cells will kill you pretty fast.
It should take around 30 minutes to go from start to surviving 300 seconds, and you actually need a different strategy to survive that long.
There’s a cheat menu that I used a lot during development to be able to set up a game with the level I wanted from start :D There is a hint on how to enable it in the description.