If you're short on time, there's only move you need to tone your butt — plié pulses.
Start in a standing position with your legs slightly wider than your shoulders, and your feet facing slightly out. Squat down, aiming to make a 90-degree angle with your legs while keeping your back straight (don't let your upper body creep forward!).
Move up and down 25 times, then stop in the down position (position No. 2 in the below photo) and pulse 25 times. After the pulses, stop in the down position and hold for 25 seconds.
Repeat three times and your muscles will be on fire!