I did not get a response from the MSC before my scheduled visit. (Not surprising: I self-assigned the shop at about 2:30 PM PST Saturday and the MSC is located on the East Coast. What are the odds of getting a smaller MSC to respond on a Saturday evening?) So, I went with my best guess: I made sure I arrived early and tried to get a table before 8:00. I arrived at 7:30ish and was seated at 7:45.
Sunday morning, I got an email from the scheduler saying that I should go ahead and conduct the visit, but to make a note on the survey about the issue with making the reservation during the stated time frame. Of course, by that point, I had already submitted the report - and there wasn't really an appropriate spot on the report to mention reservation issue.
I anticipate that it will be just fine.
Hard work builds character and homework is good for your soul.