If you waste to much time online---TRY THIS OUT!!!
The site above has a download Called Lock and Rest that has really helped me break my hyperfocused time wasting periods while on a computer.
Its the kind of thing that makes you periodically think about what your doing because it locks you out of your computer for a user determined amount of time. You can tell it to make you take a break for anywhere from 1-60 mins. I do 10 min breaks because it helps me a lot...
Ussually when the immage pops up I get out of my chair, take a break, and I will do some sort of quick burst of physical movment- like running up and down the stairs quickly or even a few jumping jacks/pushups. - doing that also really helps my mind get into gear to stop wasting time. So try it out and see if it helps any for you.