I am a host with Wal-Mart pricing. We are very flexible on arrival times - 4-midnight - but we need to have a reasonable expectation of when they are going to be here so we can prepare our own timetables and greet them.
If, for example, a guest is coming in from overseas, or through heavy traffic, we can pretty well bank on a sustantial delay and plan accordingly. Guests arriving after midnight can check themselves in and a snack will be waiting for them.
Yesterday at noon a guest booked on IB for arrival "this afternoon'. By 3PM I still didn't know when he was arriving so I contacted Air. They could'nt reach him either. By 5:30 I advised the guest that I would be cancelling, adding that Airbnb would provide him with an alternate host. I finally heard back from him. He'd be here by 10PM. A 10-hour wait for a $22 booking.
No, thank you.
I just got another request from a new guest 4 days from now. She said she wasn't sure when she would be here but "she will let me know when she knows." Who wants to put their life on hold for a full day on a long weekend while she figures this out? I asked her to let me know when things firm up, and book then.
Guests give samples of their behaviour. Guests who arrive 3 hours early or late are inevitably inconsiderate in other areas, too. at least, that's been my experience so far!
Cheers!