I don't remember the name of the aftermarket firmware I run in my eonon that's in my e46 but it was like getting a new radio when I switched to it a few years ago.
If I have driven the car any that day boot time is zero seconds. Really zero aka instant on.
If its the first time I have driven the car that day it takes about 20 seconds to boot the sound and main part and another 30 to bring up nav if I had left it on nav.
Love that firmware. If I get around to fooling with my e46 before I forget about this post I will see what firmware I am running
