Hi
Can’t answer your question specifically, but I do recall that when using my polar aligned Vixen GPDX mount fitted with my Pentax KM 35mm SLR, I could take 10-15 min unguided exposures with 135mm and 200mm telephoto lenses.
You should be able to take longer exposures near the South Celestial Pole (smaller arcs of movement) whereas nearer the Celestial Equator, the stars make larger arcs in the same period.
When I first started 35mm film astro photography, I found
Astrophotography for the Amateur by Michael A. Covington an invaluable book.
Cheers
Dennis