From my own research the majority say 7 hours minimum is okay and 8 hours is better and 7 to 12 hours is optimal. Case studies of people that average 3 to 4 hours and others where age will differentiate the numbers. So forth and so on.
Internet Marketers may be a different animal? I have not seen any case studies to that effect.
As an Internet Marketer or someone not involved in internet marketing that spends a lot of time on the internet...
How many hours do you sleep?