I like the fact that this stage is seperate though, it gives players the chance to learn the cart mechanics without wasting the previous 2 stages of progress. By being introduced to this unique cart track from the beginning players should learn it pretty fast and with that in mind perhaps the lengthening of the rounds was a bit unnecassery.
There's nothing wrong with short and sweet rounds, although it does make death more of pain in the arse as the ratio of time spent dead (20s) to the round is much shorter. Making the punishment for death huge, despite the fact that players are more inclined (if not forced) to throw themselves at the cart in order to save progress. If the rounds are short and sweet, perhaps it's worth bringing the respawn wave timer down from default to 12-16s. Or at least modify them respectively to cart progress.
A Boojum Snark: Don't listen to grazr he is probably drunk