It should take about 35 minutes from the time the bus pulls out of the airport to arrival at the first WDW drop-off.
Add to that time (15 minutes?) to get off the plane and get to Magical Express (if you're not stopping for luggage).
Unknown amount of time to wait for the bus...I've never waited longer than 20 minutes and have on occasion gotten right on a bus which left right away...but I usually figure 15 minutes...
You also never know which resorts they'll go to in which order...AKV could be first, second or third stop ... so figure, at 10 minutes per stop (and time between resorts), another 20 minutes in case you're not first...
So...a good "rule of thumb" is to figure on 90 minutes--knowing it could be 30 minutes longer or shorter...
So, if you're plane arrives on time, at 4:30, you should be at AKV by 6:30, and possibly sooner...
Check-in is pretty quick, and that time of day there's a very good chance your room will be ready--maybe 10 minutes from getting off the bus to getting into your room?
So, if you're going to eat at AKV, I would think a 7 p.m. ADR is pretty safe...
You should have no trouble at all making Illuminations...even if "everything goes wrong" and it takes a lot more time than the averages...you could probably even make a 7:30 or 7:45 reservation at one of the Epcot restaurants...
Hope that helps...
Have a great trip!