At present, Automatic Check In occurs if a booking is made on the day if the check in period has started. However, if a user books on the day, get automatically checked in but doesn't turn up that desk gets wasted, because the user doesn't get bumped and it allows a user to cheat the system. Also, the text in the application set up says that "Bookings made after the check-in period ends are always checked in automatically, regardless of this setting" which is incorrect according to support. I've also got examples of users being automatically checked in when they book several hours prior to the check-in window, so it isn't working as expected.