Do you really think that you would have time to break your concentration in an emergency and say "I think its time for you to leave"?
No is the answer, as that would also jeopardize the safety of the person in the jumpseat.
They don't have 5-point harnesses in the jump seat for the person to leave when it gets bumpy, and passengers travelling jumpseat for the duration are always given their own safety procedures by one of the pilots.
If the plane is evacuated, then everybody is evacuated including those in the flight deck, so that shouldn't be an issue.
That is what should generally happen.
True?
SFly