If this is to do with shipping and transport, then lay days or lay time is the time necessary for loading and unloading before the ship sails, or before the goods can be transported further after the ship has berthed.

Costs run up, of course during this time, and if the ship is unduly delayed, the costs may be called demurrage.

I don't know if that helps - if not, please give some more details of the context.

Lyng Svensson: Samfundslitteraturs Økonomisk Ordbog
JH Adam: Longman Dictionary of Business English