I can't find any mention of doing multiple sets in the epic abs workout, however the built in timer has a rest period after the last interval rather than ending.
I see it this way: there are 9 exercises, 20 seconds each. You do them one after another with no rest in between. That makes it a 3-minute hardcore HIIT workout. There’s a how-to video under the workout's description (scroll down to see it) as well, have a look and enjoy the workout!