Also each lap is dedicated to one activity, first is manufacturing where I work on my project (the actual coding part), second is traffic (this is the dreaded marketing/outreach part) and finally is the optimization part (seo, increasing conversion rates, improving design, etc).
I've seen that the diversity of this work prevents you from getting bored and also is very good for your sites because if you keep working on just coding your sites seldom make any money.
The 3 hours limit is because after that i can happily watch tv, spend time with my family or just work on my other hobbies besides computers guilt free.
P.s. When you try to do as much work as you can, i believe you still only get 3 hours of work done - yet you feel guilty of not doing enough which causes unhappiness.