Arrivals before the check-in time are not possible most of the time based upon cleaning and maintenance requirements. Departures after the check-out are generally not permitted for the same reason.
This restriction sometimes comes as a surprise to people who are used to staying in hotels, motels, and resorts. Please try to appreciate the stark difference between the work involved in properly cleaning a private residential home and the time required to clean a much smaller hotel room. It can take up to 6 hours to clean a private residence (Hence the reason for the 6-hour gap between check-out and check-in time). Moreover, homes require routine and special maintenance, which must be completed between occupancies.
In the rare event that an exception is allowed to the established times, there will likely be a fee charged by the landlord.
The only way to be certain of an early arrival is to purchase the night prior to your arrival. The only way to secure a departure is to purchase the night after your scheduled departure. Please, call your host if you wish to arrange and pay for any additional nights.