I can’t tell if the camera frame rate changes over the course of the clip, but if it was my design, I’d make the “opening” rotation as fast as possible (minimizing drag while accelerating) and then close it with a slower rotation to act as an air brake to let my drivers brake later.

I’m guessing their exhaust deflector plate also plays into their rear wing and active aero performance. It looks engineered to help the flow reattach more quickly as it is closing. It may also play into some effects of its aero while the flap is inverted.