The Cotton Division shall deliver bills to all persons from whom payment for fees or expenses on account of services under this subpart shall be due. Such bills shall be rendered as soon as practicable after the last day of each month for the amounts due and unpaid on such day. When necessary, in the discretion of the Area Director or the Director, any bill may be rendered at an earlier date for any fees and expenses then due by the person to whom such bill shall be rendered. Payment of any such bill shall be made as soon as possible after the rendition thereof, but in any event not later than 2 weeks after such rendition.