I have never done interviews during the daycare day. Mostly due to the fact that I don't know them from Adam, and I don't feel comfortable with strangers around the daycare kids. As a parent, that is how I would/do feel, anyway. I have had one person come back for a playdate-visit during daycare hours. I think that it makes sense to do so. But I only do it on request.
So far I have been pretty lucky for not being strung along by anyone. But I do make it clear that I am not waiting around on them. I ask for a response in a timely manner, and if I have not heard within a few days (even a "we still have a few more to check out, haven't decided yet"), I cross them off.