I was doing a kettle bell ab workout last winter. It only took about 10 minutes to complete but it left me whipped.
Yeah, I do reps of 15. Put a rep in, go do something for around the house for 5-10 min, back do another rep or two, back to another chore. Easy to work in schedule, don't need much to accomplish like I do to go for a bike ride.
I took a class last winter for 3 months then decided to buy a few and do the routines on my own. That slowly slipped away over the summer but I plan on getting back in to it. There are some good workouts on you tube to follow along with.I loved it when I did it though, it really kicks your butt.