It's amazing how quick matches went by back in the day. I wonder how many matches Steffi won in under 40 minutes.
I think it all depended on how much stalling the opponent did.
A quick search of the scriptorium yields some information (and another great Steffi the Smart-Ass quote, this one from 1989 San Diego after beating Kohde-Kilsch in 42 minutes: "Was it that fast again? Oh no."):
From 1987 Boca Raton, def. Kanellopoulou in 35 minutes and def. Gomer in 34 minutes.
From the 1987 Lipton, def. Keil in 38 minutes and def. Bonder 36 minutes.
The infamous 1988 French Open final, def. Zvereva in 32 minutes.
1989 Mahwah, def. Kessaris in 32 minutes.
1989 USO, def. Phelps in 37 minutes.
I know there are a few more, but haven't these poor girls already suffered enough?