Personally, I dont worry about initiating "dormancy" in Mexican Pinguicula. If their leaves change to succulent, I move them out of trays and keep them dry and humid until they start producing carnivorous leaves again. I have been growing a few species for 4 years that have never seen a dry period with succulent leaves, and no signs of slowing down.
My lights are on for 13hours in the summer, and 11 in the winter. If you look at their natural habitat, there is little change in day lengths. They do experience a much drier and cooler winter though. My temperatures are around 80F days in summer, and 70F days in winter. Nights range from 55-60F in summer, to 40-50F in winter.
www.pinguicula.org has some good graphs from the different areas each species comes from, which is a good reference for temperature and rainfall.
This is a good link for day lengths. http://www.gaisma.com/en/dir/mx-country.html