My company designs and supplies equipment to contractors. The first thing we do after receiving an order is generate an engineering submittal, which can take up to 6 weeks of labor. Then the customer approves it, or asks for corrections before approving it. This approval is our first billing milestone. So when setting a "Date Labor or Materials Last Delivered" in zlien, do I use the date on which we begin expending labor? Or do I use the date that submittals are approved, which is the date where the customer believes they've actually had something 'delivered' to them? Note that our company does business all over the US (and internationally).