@Donna1251 The check-in is only "late" if it's after 11 PM.
Each time a booking is confirmed, I recommend asking the guest to schedule their arrival time, like an appointment, to be sure someone is there to let them in. If they haven't responded by the day before arrival, try calling or texting them (sometimes Airbnb notifications get lost in the spam folder). You want to get this squared away before the arrival date arrives, because then they may be in transit and not able to send/receive messages.