Does the back up camera activate quickly upon puttng the car in reverse at startup?

yes, I have an aftermarket camera that activates once the car is put in reverse even if the system is booting up.

Thank u very much for ur reply.

its not instant, but it will turn on after a couple seconds durring boot up, there is a point however if allowed to get far enough durring boot up that you will have to wait until its finished

Most people on this site have reported, including myself when I had the F90BT, that it takes way too long for the cam to display when the vehicle is put into reverse from a cold start. In my case and others, it took around 15 seconds or more and sometimes would not display at all. Most of the time I was able to have my car reversed from a parking spot and in drive before the cam would display.

even after the 3.1 update?

I have seen some complaints on this forum of the problem that still exist after the update.