Oracle Bills of Material computes the fixed and variable portions of manufacturing (processing) lead time using routings and detailed scheduling.

• Fixed lead time: That portion of time required to build an assembly that is independent of order quantity—for example, setup or teardown.The fixed lead time is calculated by scheduling a job for a quantity of zero with the current date as the job start date.
  Because all lead-time offsetting uses the fixed and variable lead time of an item, the processing lead time represents an estimated lead time. Processing lead time represents the typical time required to build a typical number of units.

Bills of Material uses the following formulas to compute fixed lead times:
Schedule a job for zero quantity beginning on the system date and compute fixed lead
time as follows:
completion date (of one item) - system date

• Variable lead time: That time required to produce one additional unit of an assembly. The variable lead time is calculated by scheduling a second job for the lead time lot size quantity, with the system date as the job start date.
  Variable lead time is expressed as days per unit.

• Processing (manufacturing) lead time

The algorithm schedules one discrete job for a quantity of zero (fixed lead time) and a second discrete job for the lead-time lot-size quantity (variable lead time).
When computing processing lead time, all calendar days are considered as workdays, regardless of days off or workday exceptions.

Processing lead time is presented in whole days rounded to the next day.

Example
For example, if for item A, you had the following data:

• Lead time lot size = 10 units
• System date = 01-JAN
• End date for work in process job for 1 unit = 10-JAN
• End date for work in process job for 10 units = 13-JAN