It takes a while. Mine's been in there for almost 8 months and some fish still won't allow it to get close. When my friends tank crashed and I took in 2 schooling banner fish, they immediately went to it and let him clean them. My yellow eye Kole tang let's him clean him every now and then and my flame angel too. My clowns and fire fish can't be bothered.
My starry blenny is at him almost every day and lets the cleaner clean his teeth, it's weird to see
But I'd say at least a month or more for most fish. That's been my experience anyway...