4:20 is near the start of Dinner service (it opens at 4 for dinner). Most likely you will be in the first "wave" of seating and it shouldn't be too bad (e.g. not enough time to get backed up yet).
Of course, this is just conjecture, so take it with a grain of salt.
When we were there last year for a 1:05? (something like that) lunch, we did wait quite awhile (30-45mins).