I have contract with contractor that has payment terms "net 15" but doesn't clarify 15 days from what date? Last day they worked? Day supervisor approved timesheet?
Where and how can I get a "list of payment terms"?
If stated as you report then this usually means from the date of the invoice. The other common alternative to the terms stated would usually state "month end date of invoice" and this means that you have to pay on the 15th day of the following month.
From the contractor point of view your question actually pushes forward another one - "Do you have to wait until the end of a job before posting issuing your invoice?"
The answer to this is no. If it's a short job then it's probably better to do so otherwise you'll spend more time on administration than your actual daily work. On the other hand if it's a long job then you're perfectly entitled to invoice at regular intervals such as every week of every month.