Hi Jackie. I'm probably the biggest CTX fan on Earth. I've had the series since it came out back in 2000 and let me tell you that I still use it constantly. You can do a lot of things with it.
About you not getting to do all the intervals on Step & int don't worry you'll get there (trust me you will). I still think that's not the toughest video of the series (wait till you try Power Circuit and 10-10-10 --Oh-my-gosh--)
I read your thread the other day when you said you were short on time at the moment and you wanted to find intense workouts you could do in a shorter amount of time. Definitely CTX is a great choice. I think you should do it like it is for 2 weeks exercising just one body part per day until you get used to the workouts and then try a 2 body part per day rotation for 4 weeks. If you like the results you're seeing do it for 2 more weeks and then go back to a Slow and Heavy rotation for 6-8 weeks, but this time use the CTX cardio portions with S&H (do the cardio before or after the weights --that depends on your preference--). If you're still short on time by then you can do the CTX cardio with just one body part of S&H per day (you'll be done in about an hour or so) if you choose to do two body parts per day then it can get longer probably an hour and half or more, but let me tell you that if you choose to do the longer one you'll be very wiped out and you'll need more rest days and you'll also need increase your caloric intake.
This is the way I do my 2 body part per day CTX rotation
Day 1: KFormat cardio, S & int chest, KFormat (biceps, abs, stretch)
Day 2: 10-10-10 cardio, PCircuit back, 10-10-10 triceps and stretch
Day 3: LL legs, AStep (shoulders), LL abs and stretch
Day 4: Rest or Yoga
Day 5: S & int cardio and chest, KFormat biceps, PCircuit abs and stretch
Day 6: Power Circuit (cardio and back), 10-10-10 triceps and stretch
Day 7: Same as Day 3
(Optional days 8 and 9)
Day 8: Rest or Pilates
Day 9: Additional rest day before starting the rotation all over again
** As you can see you get to workout 2 body parts per day, you never workout two big muscle groups on one same day (you get one big muscle group and a small muscle group i.e. chest with biceps, back with triceps, and legs with shoulders) and you never workout your abs two consecutive days. ** This is how I do it. I thought I'd share. Have fun!