When Should the Pick Start?

Ask a warehouse how it decides what to pick next and you'll get one of two answers.

Either "we work through them in the order they came in." Or "we run waves."

Both are perfectly reasonable. Neither one actually answers the question.

The order they came in

Think about this for a second.

An order that landed yesterday afternoon for a delivery tomorrow morning is nowhere near as urgent as one that came in an hour ago for a truck leaving at eight.

Sorting by arrival time sorts by the one thing that has nothing at all to do with when the goods need to be on a vehicle. And every warehouse doing it is quietly relying on a supervisor to override the queue from memory, several times a day, forever.

That supervisor is usually very good. They also go home at some point.

Waves are better. At a different question.

Wave picking groups orders into batches released together, normally to smooth out labour, line up with a sortation window, or match a carrier collection. It's a sound technique and it does real work.

But here's the thing: a wave is a warehouse idea. It answers "how should we group this work so the floor runs nicely". It has nothing to say about "when does this particular order need to start so it makes its truck".

Which is fine right up until a wave contains orders going out on different runs. Then the whole block releases at once, an order for the 07:30 departure sitting happily next to one for the 14:00, treated exactly the same. The floor works through it in whatever order it picks things up, and whether the early truck gets away on time comes down to luck.

The right way round is backwards

And it's simpler than it sounds.

Start with when the customer needs it. Take off the drive time for that route, and now you know when the truck has to leave. Take off the loading window. Take off staging.

What's left is the last possible moment you can start that pick and still make it.

That's a pick-by time, and it belongs on every order in the queue.

Sort by it and the floor works the day's actual promises in order, on its own. The order going out on the early run rises above ones created before it. When three runs are in progress with different departure times, you can see at a glance which picks are tight right now and which have room. Nobody's cross-referencing a manifest against a delivery schedule in their head.

One catch. Every number in that calculation - the route, the drive time, the departure - lives on the transport side. None of it exists inside a warehouse system that stops at the dock door. So a warehouse working on its own simply cannot produce this, no matter how well run it is.

Fifteen minutes is a lot more than it sounds

It's tempting to file this under fine-tuning. It really isn't.

In a 2023 study in Production and Operations Management, Rijal, Bijvank and de Koster modelled warehouse operations and vehicle routing as one problem, tested against data covering more than a million picked units. Widening delivery windows by fifteen minutes cut total costs by 4 to 6 percent.

Fifteen minutes. That's how tightly the warehouse and the trucks are tied to each other, and it's far finer than a nightly file transfer or a quick chat at handover can resolve.

The bit I'd tell everyone

When a warehouse starts missing departures, the instinct is to push. More hours, more bodies, a louder supervisor.

Research published in OR Spectrum in 2024 on cutoff-based shipment promises points somewhere else entirely. Mohring, Jacobi, Furmans and Stolletz found the thing that decides whether a warehouse hits its deadlines isn't demand variability or processing variability. It's utilisation.

In plain terms: when the floor is already busy, what determines whether the truck leaves on time is the order you do the existing work in. Not how fast anyone moves.

Sequencing is the lever. Effort isn't. Which is rather good news, because you can change sequencing on a Tuesday afternoon. You can't hire your way out of a bad queue.

Catching it while you can still do something

There's one more thing a pick-by time gives you that neither arrival order nor waves can.

If that time passes and the pick hasn't started, the system can put a hand up. While there's still room to act. Move someone across, split the pick, or make the call to hold that order for the next run.

Without it, you find out when the truck leaves late, or when a driver turns up outside the window and the customer rings. By then your only remaining option is an apology.

The short version

Next time somebody asks how your warehouse decides what to pick next, the good answer isn't "in the order they came in", and it isn't "in waves".

It's "by when it has to be on a truck."

Everything else can sit happily on top of that. Batch it, wave it, zone it, whatever suits the floor. But underneath, the queue should run on the promises you've already made to customers, not on the order people happened to hit submit.

And if your warehouse can't see those promises, that isn't really a warehouse problem. It's a wiring problem.

How this runs on one platform

In Depot WMS, the fulfilment queue is sorted by pick-by time rather than by order entry. The system works backwards from each delivery commitment through transit, departure, loading and staging, and puts a pick-by time on every fulfilment order in the queue.

That only works because the dispatch plan and the picking queue aren't in separate systems. Committing the plan creates the warehouse picking work and the driver trips in Cargo TMS at the same moment, so the departure times the queue is built around are the real ones. And when a pick-by time passes without the pick starting, the order gets flagged as at risk before the departure window closes.

Which means nobody has to work out the right order each morning. It's already the order.

Frequently asked questions

When should warehouse picking start before dispatch?

Work backwards from the delivery commitment. Take off transit time to get the vehicle's departure, then take off the loading window and staging time. What's left is the last moment the pick can begin and still make the truck. That pick-by time, not the order entry time, is the right basis for sequencing the queue.

What is a pick-by time?

The latest moment a pick can start and still make its vehicle's departure, worked backwards from the customer's delivery window through transit, departure, loading and staging.

Is wave picking the same thing?

No. Wave picking groups orders into batches released together, usually to smooth labour or match a collection window. It answers how to group work, not when a specific order has to start. A wave holding orders for two different departures treats both identically.

Why can't the warehouse work this out on its own?

Because every input comes from the transport side: the route, its transit time, and the vehicle's departure time. A warehouse system that stops at the dock door doesn't hold any of them.

References

• Rijal, A., Bijvank, M., & de Koster, R. (2023). Dynamics between warehouse operations and vehicle routing. Production and Operations Management, 32(11), 3575-3593.
• Mohring, U., Jacobi, C., Furmans, K., & Stolletz, R. (2024). Managing cutoff-based shipment promises for order fulfilment processes in warehousing. OR Spectrum, 46(2), 513-543.

This is one piece of a bigger picture.

Pick timing is one of two places where the gap between a warehouse system and a transport system shows up physically, on the floor, in front of a customer. The full piece covers both, along with the research on what keeping them apart actually costs.

Come and talk to us about closing that gap

For media inquiries, please contact:
contact@illuminate.ae