We have no idea I believe. The closest information that I know of is the following:
It suggests that Hanzo's followers were trying to kill Pain not too long before Jiraiya arrived. Perhaps a month, year, or more could have been that period. And Hanzo was killed before that.
Yet there were 2 teams from Amegakure( Team Oboro and Team Shigure) during the Chunin exams that didnt have the slash across their headband, so does that mean that Pain wiped out Hanzo and his followers during the timeskip?
It's possible that Pain sent those genin there to keep up the appearance that nothing had changed, and also why would they have a slash through their headband? It isn't like Pain had a real reason to change the headband and that all previous genin were to be made missing ninjas.