What is the soonest before movie time can we get there to be seated to eat in the theater?

It depends on the day and time. I always get there 30 minutes before the feature starts.

About 30 minutes

Blockbuster movies that have sold out shows will be seated as early as an hour before the movie is set to start. Otherwise it's usually 30 mins ahead.

I usually arrive around 20-30 minutes before showtime, have a drink in the lobby and go in 15 minutes before it starts. You still have previews before the movie as well so you can order then too.