In CIRCULATION > CHECK IN, there are two checkboxes in the Options section:
* Forgive Overdue Charges
* Dropbox Mode (Book Drop)
These are two separate functions that can be used independently, or in conjunction. The Forgive Overdue Charges allows checkins without fine acccrual, regardless of how late the item is. Dropbox Mode simply sets the checkin period back one business day, to the last business day the library was open, based on the Koha calendar for that library.
-Mickey