Thanks mate
I powered up my FDIM (single zone as can be seen, no SAT NAV) and I took some timings:
Powers up and starts displaying (lights up the screen) within 24 seconds. Splash screen on/off doesn't matter, except with the splash it takes a bit longer to display the above.
Now to the newer firmware on the newer unit...
It takes 19 seconds to turn on the screen. A bit faster! But, it always shows the splash screen on first power-up. It does this for 10 seconds, turns off, then there's some extra time before it will turn on again and display the above.
Maybe the new firmware turns on the screen while the CPU is doing very little, almost sleeping, so capacitors continue to charge at a faster rate? Only well after 30 seconds does it run both the screen and CPU. A 7 second increase. I don't think the SAT NAV makes a difference, because the newer screen often didn't show the "Nav" button until well after the screen was started and was running for some time (quite a few seconds).