Because only the check-in START time was listed on hotels.com, it was only after booking that I discovered there was an end time. In fact, 'twas only after traffic hold-ups forced me into a services on my journey down...
Fortunately, the gentleman I spoke with on the phone was very pleasant, understanding, and able to offer a solution that meant I was still able to enjoy the room despite ultimately arriving around midnight. The peace and view of the location was gorgeous, the room spacious, the bed comfy, and the shower fulfilling.
My only slight grumble was that breakfast didn't start till 8am the following day, meaning I had to set off again before taking advantage of that (previous B&Bs have offered me a 'grab-and-go' bag in similar circumstances). But if I'm ever down in this direction with more time on my hands, I'll be sure to check the availability here first.