The Snowperformance.net kit is already activated by a boost-controlled relay, but I was wondering if adding an additional relay could be added without losing too much response time. The reason being is that I want to be able to turn off the system via a switch mounted on the dash. The small dash switch, IMO, won't be able to handle the current to the 200psi pump.

I guess all I am really asking is how much time does it take a normal Bosch relay to activate?

a few tens of miliseconds. pretty damned quick, in other words.

It does activate pretty much instantly. You could put the switch between the ground for the pump.