The original had you on a timer, but also with better level design and just bigger levels in general. They had you relatively boxed in until you reached a certain size, than you could break through to new areas.
I wanted to do similar with this, but it wasn't really feasible with the setting I'd chosen. Because of the comic, you start at size "car", and the biggest things I could think of were trees and buildings. Would be fun to do some more experimenting with the concept.