The "Arrival & Departures" report allows you to see guest fluctuations for a particular day. To see the report, navigate to Reports > Arrival & Departures. The overview tab "All Bookings" shows up as per default.

Select a date to only see changes for this particular day.

 The "All Bookings" tab gives an overview of the day's due check-ins and already checked-in guest and their details. A click on a booking you number brings you to the particular booking.

The tabs "Due Today", "Checked In", "Leaving Today" and "Checked Out" display the upcoming check-ins left for the day, who is check-in already, the upcoming check-outs for the rest of the day, and who has check-out already, respectively.