I would expect you to be seated by 7pm. maybe earlier but not a ton
the odds of you being seated at 6:20 are extremely slim
this restaurant tends to run late
I would also suggest requesting your check with dessert if you are in a hurry to leave. One of the reasons that I will never dine here ever ever ever again is the hour it took to get the bill and then another wiat to get our cc receipt back
I would expect you to be on the monorail by 8:30ish
If getting back to the park is a priority you may want to consider CS that night