What is the difference between queue time and lead time?

Lead time is the total elapsed time from order release to completion. Queue time is the portion of lead time spent waiting in front of work centers. In most shops, queue time is 70–90% of lead time, which is why work-content estimates almost never match quoted lead times.

How do I reduce queue time?

Three levers: (1) release less work — match release rate to bottleneck rate; (2) sequence the bottleneck to minimize setup loss; (3) protect the bottleneck with a small staged buffer instead of a giant pile of WIP. These three changes together typically cut queue time 40–60%.

What is a healthy queue time?

At non-bottleneck work centers, near zero — work should be processed within a shift of arrival. At the bottleneck, a deliberate buffer of 4–8 hours of staged work protects against upstream variability without inflating lead time. Anything larger is excess WIP.

Queue Time — Manufacturing Scheduling Glossary

Definition

Queue time is the elapsed time between when a job arrives at a work center and when the work center actually starts processing it. In most discrete manufacturing shops, queue time accounts for 70–90% of total lead time — far more than setup or run time combined. It is the largest, most controllable, and most ignored component of manufacturing lead time.

Why it matters

If a job has 8 hours of work content and a 6-week lead time, queue time is the difference. Customers experience queue time as long delivery promises and unpredictable due dates. Reducing average queue time by 40% — which is achievable by sequencing the bottleneck and starving non-bottlenecks of WIP — can cut quoted lead times in half without adding any capacity.

Common failure mode

Planners release work to "keep the floor busy." WIP accumulates in front of every work center. Average queue time grows from 2 days to 8 days. Lead times quoted to customers grow with it. Nobody links the lead-time inflation back to the release policy, so the shop hires more capacity instead of fixing flow.

How Skody approaches it

Skody tracks queue depth and queue time per work center in real time, and uses it as an input to release decisions. Work is released to the floor at the rate the bottleneck can consume it, which holds queue time at non-bottlenecks near zero and dramatically shrinks total lead time.

Bottleneck

The resource whose limited capacity governs the throughput of the whole factory.

Work Center

A grouping of one or more machines or stations that share routing and capacity.

Finite Capacity Scheduling

Scheduling that respects the real, limited capacity of each machine, operator, and tool.

Manufacturing Variability

The unpredictable variation in setup, run, and queue times that makes plans drift from reality.

Dispatching

Telling each operator and machine which job to run next, in what order, right now.