Let's be clear here BC I am advocating resuming play or variation of.
I was disagreeing with the notion that the laws require a game to be extended for the taking of a PK so therefore this must apply to FKs as well.
The problem I foresee with your 10-20 seconds is that is plenty long enough for someone who remains aggrieved to exact revenge and cue more mass brawling.
If there's a fight or chance of a fight, and time is all but done, we're going home with less paperwork in my world.
I would however be blowing for the FK to be taken, immediately followed by the FT whistle so that no more play actually occurs. And obvs all misconduct will be dealy with accordingly.