It's been a good year or two since my experience. Jumping on my knees wasn't what you would call a graceful act. And it took a little getting used to, I remember using my arms more to jump. That's the funny thing about the mini-tramp. If you start whereever you can, you will always improve and be able to do more the next time.
By the way, you can break up that 40 minutes any way you want.