It's really hard to say how long it may take. In my experience, the 'feistier' rosy boas are easier to switch, while the more passive ones seem to need the additional
inspiration of a live pinky, in part because they're more uptight about human presence. That's terrible that the pet store gave you false information- did they say why
they refuse to sell them live? Is this a Petco? -or similar shop that thinks all rodents should themselves be pets? What a shame...