A delivery window is the time range when a customer can accept a delivery: a restaurant before lunch prep, a school before the kitchen opens, a store before its receiving door closes.
Windows are one of the main constraints in route planning. Two stops close together on the map can be impossible on the same route if their windows do not overlap. Missing a window can mean a refused delivery, a second trip or a kitchen that runs short, so planners usually treat the tightest windows as fixed and build the rest of the route around them.
The APFoodz route builder plans around each customer's delivery window.