You might be able to make it, but you won't enjoy your meal. The food will be on the buffet when you're seated at 8:00 (or by 8:10). And you can eat and be done by 8:30 to head to the monorail. But you'll be rushing your food, and you may not have seen all the characters by then. Even though the restaurant opens at 8:00, the characters don't come out for the first 15-20 minutes (I've had an 8:00 seating a number of times). Based on my experience, you can be comfortable done eating and see all the charcters by 8:45 - 8:50.
By the time you get to the monorail station, and wait for the 2nd or 3rd monorail because the monorails are full by the time they get to GF (Contemps that don't want to walk to MK, Poly guests going to MK, and probably some TTC people that think they can beat the MK monorail by taking the resort monorail), and then get through security, you'll likely be in MK by closer to 9:30.