How long before an operation is pre-op?

I have been to see a specialist about an issue and he has put me on a list to have an operation. I have received my letter regarding a telephone pre-op appointment in early May but as yet have heard nothing about a date for the actual operation itself. Is it likely I will know the date of my operation before the pre-op appointment or will I only know after the pre-op?

I always thought pre-op's were done only a few days/a week before the actual operation.