I am not sure that you do need to reduce development, at least Ilford's technical data sheet doesn't indicate anything other than increased exposure. Here is the data sheet: http://www.ilfordphoto.com/Webfiles/...1054152313.pdf

I have never personally changed development due to reciprocity failure alone. I have changed development and exposure times to compensate for night conditions which are very contrasty by nature, but it does not sound like you are talking about that kind of situation, rather you are encountering long exposures due only to the small aperture of your pinhole camera.