It is mentioned in the Circular of Information which is prepared jointly by AABB, the American Red Cross, America’s Blood Centers, and the Armed Services Blood Program.
https://www.aabb.org/tm/coi/Documents/coi1113.pdf
"Aseptic technique must be employed during preparation and administration. If the container is entered in a manner that violates the integrity of the system, the component expires 4 hours after entry if maintained at room temperature (20-24 C), or 24 hours after entry if refrigerated (1-6 C)."
"Transfusion should be started before component expiration and completed within 4 hours. "
Not sure where the 30 minutes comes from. Some institutions have used "promptly" and then have gone on to define what promptly means, i.e., 30 minutes, 20 minutes etc to allow time for patient identification etc.