Band practice time - timing issue

The ceremony is outside under shade trees about 50 yards from reception building (dance hall) Mariachis begin ceremony music outside at ceremony site at 5:30 when guests start arriving. Procession to start at 6 putting the ceremony to end around 6:30. Mariachis playing until 7 when we do the grand entrance into the reception building.


We have a band that will be ready to start at 7 inside the reception. They need some time to set up, tune their instruments, practice a little bit for sound check. The contract says they need to be able to arrive up to 2 hrs in advance to set up but the time will vary. This is fine, they can come whenever they want. I'm not exactly sure how much time they need to sound check but I was in a band once and it could take 10 minutes to an hour.
However, I'm afraid their practicing will be heard during the ceremony and/or will intrude with the mariachis. I want to ask the band to arrive around 5-5:30 so they can set up and sound check before the ceremony at 6. Then they can eat (the buffet will be set up and ready) and chill out before the guests start trickling in between 6:30 and 7.
Is this being too controlling? Am I needlessly worrying about it? Any different ideas?