Could we have a kind of time limit - that could be set by us - that can be spent on SO?
When overflowed, that time limit would have the next SO page display a big Warning, something like
You spend too much time on your computer and should better go outside (...) or continue your work tasks [for which you are paid] (...)
The way to count the time would be based on the intervals between page changes - if for instance that interval is less than 20 minutes. When an answer is being responded, the time is counted even if > 20 minutes (thanks to Ajax calls, SO knows that you are responding...).
Just an idea ... before to go outside!