Here's an option. The DJ should be able to set up his gear along with the band's. He could then either stay or go elsewhere ( MOST are going to charge you extra for this - I would NOT!). He MIGHT DJ during band breaks or not as well.
When the band is done he can then begin right away.
In one wedding I did, there was an accoustic duo who played 3 hours, and I got with them and used MY sound gear (except for mics and such), did the basic set-up and allowed them to adjust it to suit their needs.
Since the wedding couple didn't really need me there for the band breaks, I went shopping since I was in the "big city" where I had lots of options.
Again, working together this way can keep the flow going, and a really KIND, UNDERSTANDING DJ will cooperate fully.