Well, who knows - but maybe a little over two.
As Strangeways was released in late September 87, just over two years would see them enter the 90s - if that's the point you're making. Strangeways was recorded in March and released 6 months later (The Queen Is Dead, of course, took even longer to appear) and The Smiths continuing would have necessitated Marr taking a substantial break too (he has always stated this was his intention). So I think you'd be looking at a 1989 release date at the earliest to write, record and release any follow up LP, if not later. Even so, Marr's concept for the next album does give you a strong idea of the direction The Smith may have taken musically.