Delivery time windows are the periods in which a customer can or will accept goods: “8 to 12”, “after 3 pm only”, the unloading slot booked at a distribution centre’s dock. They turn every stop from an address into an address with a time attached, and they’re the constraint that most often breaks a route built by hand.
Hard and soft windows
A hard window can’t be missed: outside it the delivery fails, because the customer is closed or turns the goods away. A soft window is a preference that the calculation tries to honour and can break at a cost. One customer may have two windows in the same day (open 8-12 and 15-18), and a low-emission or restricted-traffic zone behaves like a window that applies to a whole area rather than a single stop.
Why they complicate planning
Without windows, you sequence stops by proximity. With them, every choice constrains the others: serving one customer earlier can make you late for the next, and unloading time eats into the slot. Arrive early and you wait; arrive late and you lose the slot. A delay at the start of the round ripples through every stop after it.
In the Vehicle Routing Problem this variant has its own name, VRPTW (VRP with time windows), and it’s what route optimization software solves alongside capacity and priorities. How to collect and manage windows in practice is covered in the guide to managing delivery time windows.
FAQ
Is a time window the same as the expected arrival time?
No. The window is a constraint the customer sets before the route is planned; the estimated time of arrival (ETA) is an output of the plan and shifts during the day. A good plan keeps the ETA inside the window, with some margin.
How do you handle a customer with two windows in one day?
Declare both exactly as they are and let the calculation pick the one that fits the route best. In OptivoRoute, multiple windows on the same stop, maximum tolerated lateness and dock slots are constraints in the library that can already be switched on.