Two clocks, not one
Production lead time runs from sample approval to goods packed and ready at the factory. Transit time runs from the port of loading to your warehouse. A quoted lead time usually covers only the first clock.
What drives production lead time
Fabric availability (stock versus custom), lab dip and strike-off approvals, embellishment, order size and the factory's line plan.
What drives transit time
Ocean routes, transhipment, port congestion, customs clearance and inland delivery at destination. Air freight is faster and much more expensive.
Plan backwards
Start from the date the stock must be on your shelf, subtract transit and a buffer, and that is your ex-factory date. Subtract production lead time and you have your approval deadline.