Above post is not entirely true. I know people who have grown for over 20 years, cloning veging and growing seedlings under 24/0 schedule. It doesn't cause hermies! ... I use 18/6 because it works and it saves power. But I don't see how you can say they need 5-6 hours rest, because it's been proven that they don't. And test have been done that shows 20/4 is best for all round growth. So they obviously prefer 4 hours dark period.
Roots need darkness to grow, but unless your using clear pots and soil / hydro system, they should be in the dark anyway (and if you have clear soil, can I have some? Might be worth money!!!)
80 day period most strains are ripe at??? Even in just the strains I have their finishing time varies from 42 to 98 days (or longer sometimes) ... I wouldn't say most of them are ripe at 80 days at all, that's way too general