It's much like going to a daycare centre during business hours. Usually, it was a quick visit- maybe 30 minutes at most. I certainly don't think it's a case of being demanding. As a parent, there is something comforting about seeing the environment that my child will be in.
In PEI, we have very strict ratios. If we go over ratio even for few mins, we are operating illegally. I not routinely offer phase ins until contacted place has started. Until child who create vacancy has left, if phase in happen, I risk lose business if new child coming, even with parent because extra child in house.

If my client want phase in, then they have to use first few week of their contract and come reduced hours - while pay for place.

You should check your regulation in case your province same as mine.

For my phase in, parent not present. Drop child and go. Can return in hour, or two or after half day - up to parent. But children not used to strangers in house and it affect their behavior and smooth run of day.

You have decide what suit you best. If I get request from parent that will affect day of current client child, I will deny and explain why. But this not drop in centre. I not have parent call in during day unless getting child early. I not able to have 5 set parent pop in and watch child play and my rule tend be, if I can't do for all, I not do for one.