@Sonia1891
Right now the listing link says your check in is 2-4pm not 4-6pm?
Several Hosts I work with have check-in windows like yours. Several things you can do:
1. Add your check-in window to the description or other details to note on the listing
2. When a guest books, add a paragraph to your Welcome Message about the check-in window
3. Add a paragraph to your Check-in message about the check-in window
4. Get a smart lock for self check-in. Manual keys will get lost or not returned by guests
"Please note our check-in window is between 4-6pm. If you know your approximate time of arrival, please let us know ."