Hummmm....I wonder if you were looking on the right page. Try this one:
http://www.legendsinconcert.com/locations/myrtle-beach/
Set the calendar on the left to September. If you let your mouse hover over the dates, you'll see that all shows start at 8 PM.
They are usually not sold out in September, plus there are always cancellations, so you would probably be able to get a seat the day of the performance.
We've been to Legends more times than I can remember, and we've always enjoyed it. Some of the "tribute artists" are better than others. Some appeal to different age groups. Others, like the Blues Brothers, are timeless. I could watch them every night. The show moves along quickly, and we always leave with the feeling that our money was well-spent.
Hope this helps!