With tube amps you're suppose to wait at least 60 seconds before flipping the standby switch off and playing through them. See here:
http://www.fender.com/news/the-standby-switch/
I have 821 rigs (I know, I got some cleaning to do) in my KPA and mine takes 71 seconds to load. I usually turn on my PC and KPA at the same time and KPA is usually finished loading before I see the Windows desktop so, for me, it's not that bad
Cheers,
jayson