I would definitely mention it if you feel like it needs to change. Parents forget that we aren't just "floatin' along" in our days, we are trying to keep x-number of kids occupied and most of us have some sort of schedule to follow.
I am not doing school drop-offs anymore, but this past school year I was. I found that some of the parents were beginning to either pop in early or show up a little later. I put a note in our monthly newsletter about the importance of staying as close to their "regularly scheduled" arrival/ pick up times. I simply explained that we had to be leaving the house at very specific times, twice a day and that if they were not able to be there by that time, they might miss us. And if people hadn't dropped off by the time we had to leave.... too bad. A note went up on the door, telling them to call my cell. (Sometimes we would go out after the drop-off)
I still have one family that has a lax attitude about it and I finally had to tell them to let me know when they expected to show up. We can't hear the doorbell in the playroom all the time, and I am not going to wait around for them all morning!