They played a full show. There are many here who know the scene much better than I. However, I am fairly certain you have nothing to worry about. I have seen DSO a couple times when an opening act was on the bill. You will get a full DSO show.
Go ahead. Be greedy. Hell, maybe you'll get more than the two sets and encore you are looking for. My first DSO show was about 6 years ago at the Electric Factory They did a 3 set recreation from 1980. Life is like a box of chocolate....