Revision of Rib Graft Rhinoplasty
The rib graft can be modified/reduced as soon as one is certain that they are looking at the final result and are sure they really want it reduced. As a general statement, three months after surgery would be reasonable to undergo the change.
You did not mention how long it has been since your rib graft. If recent, then swelling can contribute to the overall size. You should give it about a year.
Revision rhinoplasty after in graft.
Revision rhinoplasty after in graft can be done in 6-12 months depending on what else needs to be done to the nose. See a very experienced revision rhinoplasty surgeon!
Revision rhinoplasty with rib cartilage grafts
How long has it been since surgery? Rib cartilage can get re-absorbed by your body with time (usually about 20-30%). Swelling also occurs after surgery. These two factors would make it wise in my mind to wait at least a year before revisiting surgery. Your surgeon needs to be able to assess your nose adequately before making any decisions to remove the grafts.