One roll test, bracket, bracket, bracket. Most films are decent to 1 second so shoot from widest aperture at 1s to narrowest aperture with the equivalent exposure values (e.g. 1s f/4, 2s f/5.6, 4s f/8, 8s f/11, 16s f/16, 32s f/32, 64s f/64) in the same light. Develop and check the density to see what the reciprocity characteristics are like. If 32s is half as dense and 64s is one quarter as dense you know what you need to do. A test like this is the only way to know for sure.
If you can't do a test roll first then bracket apertures at 60s instead. Shoot f/4 at 60s to f/11 at 60s to be sure you get something. Heck, shoot f/2.8 to f/32 if you have time.