Aside from our initial visits/ interviews, I have not had anyone opt to do transitional days.
If they did, they would be paying regular rate. I have my clients pay on a monthly basis, and it really holds a spot, as opposed to being an hourly or daily rate.
I certainly see the benefits on transitioning slowly, from all viewpoints. But at the same time, a drop off and go starts us off on the right foot; meaning, if mom shows up and stays for the first few days or a week, then we are just going to deal with separation anxiety at a delayed point in time. Does that make any sense? If the kids know from day one "when I come here, mommy and daddy do not come in" then it seems better for everyone.
If I had parents that were very concerned, my suggestion is to do what spixie33 mentioned. Start off with smaller time periods and early pick-ups.