"How long does it take the 'priority' button to work...it seems to be a press...."
This is an inappropriate public venue to share flight control operation in this detail.
Terrorists frequent forums like PPRUNE to further educate themselves on aircraft opeartion.
Please don't feed their sick agendas.
My carrier lost two aircraft on 9/11. We are very sensitive about this.
If this guy needs detailed info, let him secure it thru official channels.