Tour | Booking Settings - Lag Days
Lag days is the term used to define the number of calendar days from when the trip is booked till the first day of departure. This is a reporting measure.

The Lag Days settings allow you to specify your own "lag days" brackets for reporting purposes.
From the Main Menu | Admin | Settings | Tour|Booking Settings select Lag days

The start and end fields determines the number of calendar days from the time of for the "lag"