We are delighted to let you know that we have released the Hotel Booking plugin update v. 4.5.0 with the line between two check-out and check-in dates added to the calendar. Feel free to update the plugin to the latest version to get the separator.
Hi Didier, You can use custom CSS to change the style of the check-in and check-out date of the existing reservation in the calendar on the front end. Thus it is possible to separate bookings visually.