Hello @Lois56,
There isn't such a setting. If you allow same day checkin all you can set is what Airbnb calls the "Advance notice" time. But that's just the time up until which your listing shows in searches done on that day. I have it set for 3pm and someone once booked at 2:45pm and asked to checkin at 3pm.
Did your co-host not see the reservation confirmation notification in that 1 hour period? If no notification was received then check the notification settings. If the co-host just didn't see the notification then that's an issue for them to address. With same day reservations allowed, extra vigilance is required up until the cutoff time passes. Then you can relax.
Any guest can stay up to your advertised checkout time. At the moment both listings have a checkin and checkout time of 12 noon.
If someone checking out at that time causes a chengeover time issue you might consider changing your checkin time to be a few hours later than your checkout time.
I rent a room in the house where I live and have checkout at 12 noon and checkin at 3pm. I have 1 night bookings almost every day so anyone asking for an earlier checkin is informed that I won't be back at the house until 2:30 so they can't check in until after that. I don't allow checkout after 12 noon. That way I have a stress free period to change over the room and have some coffee time in the middle of the day too 🙂
Steve.