How quickly does bronzing occur?

[CB360T_imp]

I am diligently looking for a CB to call my own. I see that bikes with even 300 miles on them have bronzed headers, so it seem to occur pretty quickly. Some bikes with several hundred or a few thousand miles have dark speckles in the bronzing and some seem uniformly bronzed. Do the speckles suggest that the bike was mistreated? Thanks.