In response to Ssj4justdale
I think you should add messages to remind people to do a break like "You played for 1 hour now, you should do a break.",
"2 hours, do a break NOW!",
"Dude, you played for 3 hours, do a break while you're still not lifeless zombie like this: http://mhviraf.files.wordpress.com/2008/10/wow-36box2-1.jpg".

What do you think?
In response to Martys1103
That is how an MMORPG named BrightShadow that I play does it.

There's this little flying cat thing that pops up in the bottom right corner of the screen every hour. At first he just suggests that you should get up and walk. After two hours he tells you to drink water. By the time you get to the five hour mark he basically tells you you've been playing too long and starts reminding you every 15 minutes after that.

I think it's kind of cute and humorous. It doesn't bother me at all and I kind of appreciate it.

The only problem I have with it is that I DO take breaks. Sometimes in excess of 30+ minutes. But I leave my character logged in and the cat doesn't check for this or reset it's timer.
In response to Zagreus
Metal Gear Solid 4 did this. I practically beat the game in one sitting and got all the masks (had to sit through cut scenes...). However, I was able to take a break for my health while the main character was busy chain-smoking cigarettes during load times. So...
I'll just create myself a counter timer to relog me every 29 minutes.
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