After 6 months on cocaine - when will the craving stop?

This is different for different people.  There is a biological component involving "resetting" of the brain's dopamine receptors which takes a week or two.  Also there is a psychological component related to environmental cues which can be quite strong and may persist much longer.  These cues relate to the situations, times of day, and company you keep, to name just a few.  It can sneak up on you.  I imagine the worst of the biological craving will be over in a week, but you can expect craving related to cues to persist for months.