Rhodium plating gives suitable white-gold jewellery a bright white surface. Because it is a surface layer, normal contact gradually wears it away.
There is no universal interval
Rings usually experience more friction than earrings or pendants, and individual wear patterns vary significantly. A warmer tone appearing on high-contact areas is a common indication that the plating has thinned.
Preparation matters
Replating should not be treated as a way to hide structural wear. The piece should be inspected and appropriately prepared first, particularly around settings and previous repairs.