What a good delivery time-window actually costs you

Time windows feel like a customer-service feature, but they're really a scheduling constraint with a price tag. Every window you promise narrows the set of routes that can legally serve that stop. A 9-11am window on a store across town from your depot might quietly rule out three otherwise-efficient routes before a planner even starts.

The naive fix is to build the route first and check windows after, patching violations by hand. This is slow and it back-loads risk: the stop you catch last is the one most likely to blow its window, because by then the route is mostly fixed and there's nowhere left to move it.

The better order treats time windows as a first-class input to clustering rather than a post-hoc check: group stops so windows are compatible with the sequence before the sequence is finalized, and treat a windowless stop as more flexible cargo than a tight-windowed one. It sounds obvious written down. It's exactly the step manual planning tends to skip under time pressure, and exactly what a solver never skips.