I recently did a 20 minute timed paper negative exposure with a pinhole camera, deep in a canyon under dim daylight, and found no reciprocity failure; the exposure time used was what I calculated from my meter reading. As long as you're using light that's blue/UV, there should be no problem.

But the real problem in the OP's situation is the wavelength of light at night from artificial light sources doesn't match a daylight spectrum.