If you go before the theater opens, there will probably be a long line. However, since there aren't usually a lot of dining package people entering the theater early, the line moves quickly and rarely fills up the theater. That's why both things can be true. A long line 30 minutes before and people walking in without waiting 15 minutes or closer before the show. That's been the case for us when we have gone.
The only thing to keep an eye on is the weather. If it might rain, you might want to wait beforehand and then get one of the seats under cover. The early show will tend to be the most full, but even then you can usually walk in not too long before hand and still find a seat.