If one inadvertently enters IMC under manual control, what is the procedure for switching this system on and how long does it take to stabilise the craft?
As per those two videos, you have two ways. Simple press the ON/OFF switch at the console (next to temp gage in video), or you press the TRIM button on the cyclic for 2 seconds or longer and it comes on (start second video for the buttons). Once the system comes on, it returns to "a nearly level bank angle and pitch attitude" immediately.