I'm a former gymnast, and we used to do ladder workouts like this at practice, though Colleen's ab routine was by no means easy. It really did take me five minutes (five minutes and three seconds, to be exact). At first, I flew through it because of the low reps, but by the time I increased my reps to nine, my core was on fire. The Pilates pumps bring the intensity of a hollow hold (if you keep your legs and chest up properly). And with that added crunch and your legs positioned similar to how they'd be in bicycle, that move alone is hard. The rocking planks and pikes will work your shoulders and your abs.
When I got to the top of the ladder, at 12 reps, I thought it would never end, and the prospect of going back down to three reps made me groan (a number of times). I managed to take just two quick breaks, even though I was tempted to take more. Colleen's ab routine is serious business, and I'll be adding it to my own workouts when I need an extra core burn. And you should, too.