In all likelihood, you're not making it.

You have 45 minutes to get off the plane, go all through TERMINAL 9, exit the terminal....walk to TERMINAL 8, pass security, and get to your other flight.

Moreover, if you miss that flight - you are screwed as the next one doesn't leave till NOON the next day.

Your hope is that the MIA flight gets changed to TERM 8. Worse case scenario, ensure you get a seat at the FRONT of the bus, as sitting in the back will decrease your chances further