The circuit for day 12 is fairly straightforward: do 30 seconds of each exercise, for a total of 3 rounds. Try to keep the rest times to a minimum, but if you're struggling, rest for 30-60 seconds at the end of each round. If you find it too easy, increase your exercise time to 60 seconds, or add more rounds.
If you're not familiar with 1-leg deadlifts, balance on your right leg and bend forwards, lifting the left leg behind you as you try to touch the ground with your left hand. Do 15 seconds on each leg.