back when I played a lot I was getting 100% rakeback and thus I wanted to play as much as possible.  This meant my concentration took some major hits.  There were a few days/weeks where I shoulda stepped away for a few days to recoup my mental capacity.

 

You talk about 6hrs a day and being able to leave and come back like that is a big enough break but it may not be.  lets say you play from 10am-1pm and take a huge down swing so you decide to leave.  you then come back at 8.  within 20 minutes you take 3 bad beats and you become frustrated.  this is a time where you should just leave for the day if not longer.

a few points:
-the best poker I played was usually after 3-4 days off
-Id suggest working out.  this may be going to the gym or joining a sports league.  Exercise is a great stress reliever.
- i also suggest that nobody rely on poker for all of their income.  if you have bills to pay then get a part time job.  poker can be so stressful at times to where it is just not worth it.