First, I have read where its a good thing to actually go 24/0 for the first week so your plant gets built up strong and quick. In the end you will see more yield. 12 hours of darkness during this early phase of growth is wasted time. http://www.420magazine.com/forums/frequently-asked-questions/129418-12-12-seed.html
I think going 12/12 from seed is a waste of time. IMHO, the loss of yield just isn't worth it. Good luck.
24/0 the first few weeks is fine, along with 20/4, I did 24/0 then after a few weeks 20/4 12/12 is for flowering, don't go there until you are ready. starting out 12/12 is crazy, that will take forever, not to mention, the 24/0 gives your plant more light, while a normal day may be 12 hours of light, the sun is much brighter, using bulbs to reproduce it, tells me that you should use more hours to subsitiute for natural light.