An order uses resources before producing a collection. Materials, processing and waiting for customer confirmation can extend this range. Reading only the date of the invoice leaves out part of the time during which the company supports the work.
It is advisable to reconstruct the real route from order to payment. For each step you can note when it starts, when it ends and which event allows you to proceed. Administrative times deserve attention when a missing confirmation prevents you from billing a task that is already completed.
In a hypothetical example, the product is delivered quickly but the acceptance document comes much later. The solution could be to collect confirmation, rather than a change in production. The point that holds up the resources emerges following the entire sequence.
I propose to compare similar orders to detect recurring delays. The duration also depends on the agreements with the customer, to be verified separately. Reducing unnecessary waiting can make the work cycle more predictable without requiring an increase in sales or available capacity.