Using your equation, it would take 270,000,000 years.
However, the information provided doesn't provide what type of Convergent boundary exists between the plates, is it a subduction zone or continental collision. It also assumes that the two plates are acting in isolation. That's not going to happen in the real world. It assumes that the two plates in question have the same consistency along the fault line. It assumes the plates 'crumple' in the same manner.
Bottom line, it's hard to say with the given information. Try posting this question under Geology.