Depending on the place, they'll give you a choice of 1-10 or more interview dates. Also depends on when you get the invite, the ealier the better. I was able to get all 4 of my west coast radiology interviews as well as 4 transitionals in the first 2 1/2 weeks of January.
Here's a tip if you are planning on doing a lot of interviews (I did 20 radiology and 10 transitional/prelim). Your best interviews will most likely be in the middle, numbers 4-10. The reason I say this is that I felt early on, I was getting used to the whole process. I scheduled places I wasn't as interested in first (late November). In early December, I had my best interviews, I was still excited and not as tired of giving the same answers over and over, but I wasn't as nervous. Then, in January (when I unfortunatly scheduled my top 2 choices), I was so tired and worn out that I really had to try hard to seem excited. I got into one of the programs I interviewed in December, so it may have been a factor.