First, follow PP's advice about getting an earlier ADR.
If you aren't able to:
If you want to see/meet the characters, you are probably SOL.
But, if you'd rather catch the parade:
Get to CP AT LEAST 15-20 min early to check in. They won't let you check in earlier than that (usually, though I WOULD suggest trying to check in earlier). This way, you might get seated earlier, but you'e very likely to at least get seated on time.
It's a buffet, so you can start eating right away, just order your drinks and ask for the check when you order your drinks. Pay your check ASAP. So, when you are done eating, you can leave right away.
Because it is a buffet, a half hour should be enough time to eat and have dessert, but you will feel a bit rushed, but it is possible.
If you are done by 8:00, you can head towards Main st. The parade does start at 8, but takes some time to get up towards CP. You won't get the best viewing location, and you won't be able to all stand together, but you will find spots to see it
You could also try to watch the parade from Frontierland. Even if you miss the beginning of the parade at main street, you could possibly beat the parade to Frontierland. After leaving CP, go left towards Adventureland. Get to Fontierland through one of the passthroughs, or around by POC. But, it will be easier to do Main St, I think.