Deirdre Bulger

Hello, I am new to contracting and have been told that a purchase MUST occur within 24 hours after a Delivery Order contract is awarded. I cannot find anything in FAR subpart 16.5 saying this nor do I see it in the clauses that would be associated with a Delivery Order contract. Can someone guide me to any FAR, DFARS, NMCARS, etc. language that would help me understand better?