Some films have extremely severe reciprocity departure. Most manufacturers have that info on their websites. T-Max 400 has very low reciprocity failure. Still you should make tests and then come up with exposures for different scenes, depending on their inclusion of light sources. I have one exposure and developing time for city streets. I haven't needed to alter that in years. If you're out there doing star trails in the wilderness, when you get the right exposure, it will work most of the time. But trial and error are necessary.

I calculate my reciprocity adjustments, such as in the studio, by find a taking reading for a very small aperture, smaller than my lens even has. For my Commercial Ektar, I find an exposure for f-90, or f-128, and then open the number of stops the manufacturer recommends. This forgoes having to change the time yet again. Eventually experience will guide you.