Almost all my stuff is done at night - or in dimly lit interiors with extremely high contrast lighting which is challenging. Obviously the larger the format, the longer the exposures will be, but even in 4x5 I would say hours of exposure are rarely required other than for specific effects, unless an exceedingly small aperture is required, filters are used etc. However exposures of at least several minutes are common, often longer. Even in 35mm I've had exposures run 8 minutes or more after adjusting for reciprocity failure. I like a lot of shadow detail though.
Reciprocity adjustments can vary greatly depending on the film and how you will develop, and how you will print so some of your own testing will be required. But to start out, if you happen to use Tri-X, TMax, Delta or HP5, Howard Bond's data is quite good.
You can also refer to Kodak's and Ilford's tech publications, but these are actually problematic. Ilford's current tables are "generic" and outdated, and Kodak's tables are sparse (some people disagree with them too).