Can non-16/18 HPV types cause ASCUS and squamous cervical metaplasia on biopsy within 3 months of acquisition, or would it take longer?   

It isn't clear that HPV causes ASCUS. I'm not sure how to interpret "squamous metaplasia" as opposed to dysplasia, but certainly many HPV types other than 16 and 18 cause cervical dysplasia, and probably can do so within 3 months of acquisition. However, I would be cautious in telling a patient that...