@Michael-and-Jacqui0 My experience has been that even guests who are fully aware of the listed check-in time when they book will still often assume an exception can be made for them. One thing I've gotten a lot was:
"I see that your check-in time is 2 PM, but I'll be arriving at 10 AM. Can I just drop off my bags and take the keys?"
I think to myself, that IS checking in, you silly goose.
If I can't offer the flexibility they hoped for, I just direct them to the most convenient left-luggage facility or nearby cafe, depending on how they're arriving. Generally these guests' attitude seems to be "there's no harm in trying," and most of them can gracefully take no for an answer. If they can't, best that they cancel the booking.