You have a prime-time reservation, so yes, I would expect to wait at least 10-15 minutes to be seated after checking in. Mealtime, especially if you want to be sure to see all four of the characters, is going to be an hour. If you just want to eat and run and are unconcerned about the characters, maybe you could be done in 45 minutes. But that won't really make any difference...
The restaurant is located in the Land pavilion at Epcot, so you're looking at a 5-minute walk to the monorail, then a 20-minute ride to the TTC, where you'll transfer to the resort monorail (and wait for it to arrive at the station), then another 20-ish minutes to get back around to the Contemporary (4th stop) from there. You're looking at a minimum of 50 minutes of travel time between the two, assuming you have monorails waiting for you at each station.
If you're driving, you have a 10 minute walk to the tram stop, waiting for a tram, getting out to your car, and getting out of the parking lot. After this is the 20 minute drive to the Contemporary, parking, and getting inside. A total of about the same travel time as using WDW transportation, a little under an hour.
So no, I do not think it is possible for you to be back at the Contemporary by 8. 9 is a possibility.