I feel like survival mode "ends" at 12 minutes. After that it's basically easy mode forever. I think it'd be more fun if it were virtually impossible to get to 30 minutes due to every monster being a sun god.
so.. in my some 8 hours of playing this 2 minute game, i've noticed that the 'nice entry' counter jumps from nonuple (9) to 11-tuple.. not sure if intentional.