Is time the reason you don't work out regularly? FB16 is what you need. The next class starts on Monday .
Try A Workout - FREEWORKOUT
ROUNDS
EXERCISE (sec)
REST (sec)
Those are the workouts shown in the FB16 Book. Check it out on Amazon.
Yes, just use "Custom" and inser how many rounds you want to do, how long you want each round to be, etc.