I add people to my wait list but I wouldn't actually ask them to come for an interview unless I have a spot open up.

I have had wait lists that were 3 people long and then I would contact them all and they would all have found daycare by then.

The wait list sounds good in theory but has never worked well for me.

I would suggest holding off interviews until you know more or else you will be wasting an hour of your time and potentially not even be able to accept the family.