It limits how far ahead a customer may choose their first delivery date. Enter a number of weeks; dates later than today + that many weeks are removed from the start-date list on the plan page. The default 0 means no limit (all upcoming open dates that match the plan's allowed start days are offered). For example, 2 lets customers start within the next two weeks only. Note the list also starts after the customer's last existing subscription delivery if they already have one.