I had a go at the start up thing and it did seem odd, that I couldn't do them very quickly, but never felt taxed doing sit ups for a minute. I didn't have anywhere to support my feet though. The reccommendation of my having a day or so recovery seemed a bit much because I never really felt that I'd done anything that warranted any recovery.
I managed 23 in the minute, so I might have a go at getting 60, just for fun. I'm not sure that supporting the feet is the way to go for an abdominal exercise, so I won't bother. I'd have thought that you would want to isolate your core strength and abs. Wouldn't having your feet supported use your leg muscles too?
As someone said in the press up challenge thread. Good technique is more important than speed. Think Charles Atlas. Speed will come in time.