Is there a way to temporarily block myself from Facebook or limit the time I can go on it?
Extension - Productivity Owl
With this nifty extension you can allow unlimited access to certain websites that help you be productive and refuse access to the biggest distractions. For all others, you can allow a certain number of seconds to get the information you need. Finally, you can set aside free time when there are no restrictions at all.
Want to be productive? "Ride the Owl"...
SmalApp like ColdTurkey could do it
I'm use chrome extension Website Blocker. Work for me. Block me 8am at 6pm.
On a Mac or using Linux? Edit your hosts file. It's easy!
Fire up Vim or Nano (I prefer VIM), find your hosts file and add the following lines.
Super simple stuff!
As others say, ther's no strictly-mechanical way to enforce just this, but you could use Eye Leo (download from http://www.pcworld.com/product/1199290/eyeleo.html) to remind you to take a break.
No but seriously, self control.