I would use a timer. Once the key is pressed, it starts playing the animation and then 0.5s later (short timer) it calls an event which tells the animation to reverse (-1 playrate). Every time you press the button, you clear that timer, set the playrate to +1 and then restart the timer. Once the animation completes (can get this from a notify), you stop all communication.
The shorter you set that timer, the faster the player has to press the button. If they run out of stamina on too long of an animation, then it will just go backwards and pick up when they start tapping again. This is better than having the whole animation reset if you’re not fast enough…to me anyway.