@David64 Since the inconvenience is now fait accompli, I recommend waiting until your review to "educate" the guests. A short note in the public review to warn hosts that they failed to communicate their change in plans, and perhaps a more detailed explanation in the private feedback about how this affected you.
But yes, I think your decision to stop accommodating this kind of early checkin is a good one. Instead, you can demonstrate your efforts to be helpful by giving these guests some great local tips about how to occupy their time after landing - the best place for a leisurely lunch, and/or a nice place for sightseeing en route to your home. (For guests getting around by public transit I suggest left-luggage facilities, but I guess most of yours are using a car).