We used to message our guests reminding them of check-out time, but after a lengthy discussion with my co-host, we both decided that it could result in bad optics for the guest, and a negative experience after what might have been a great stay. Sending a reminder about the check-out time could be construed as ushering them out, as if they're not an important customer, and all you care more about the next one coming in. Instead we've opted to include the checkout details in our check-in message(s) as well as house manual, and we've also posted a sign on the back of the front door which says "check-out time is at 10:00am". Since then, we've had a lot more positive feedback from guests departing.