For breeding pairs I give 11~13 hours of light... more or less seems to affect breeding...
For "pet fish", in my expience, as long as it's been lite for 30 minutes before feeding, it really doesn't matter...
My lights come on at noon and stay on until midnight... because that's the 12 hour span that works best for me...
I used to have the fishroom on from 4pm to 4 am... but I found myself staying up way to late on work nights...