My experience is involved with the painting of ships preparing for the rigors of salt water exposure. The rules of the BUSHIPS Manual are to immediately acid wash all bare metal, then cover with two coats of primer, then get a finish coat (enamel) on within 24 hours of the second primer coat. The second coat of enamel can wait for months. As pointed out in other spots in this thread: Rust starts instantly as soon as any ferric compond is exposed to oxygen. Primer does not seal from oxygen, it allows the finish coat of paint to adhere to the metal. The finish coat seals out the air. In the case of the weights, I don't know if I would reblast, I think I would just do the yellow, however, when the rust begins to show, and it will, I would redo as per the above.
Bill