To my knowledge, most if not all levels are timed and they aren't just "roll crap up." I remember playing with my (now ex) girlfriend in college and everyone couldn't beat this one stage where you had to roll up a ton of geese. So I was all, "gimme the 'troller!" I whipped that stage up so bad 😉.
But yeah, if I remember correctly, they're all time-based and most have objectives. The demo was simply a "see how big you can get in 3 minutes" thing, where typically you have to get a certain size using 'x' object, get a certain amount of 'x' object or just getting to a certain size.