From the FAQ:
In my profile, what is noprocrast?
It's a way to help you prevent yourself from spending too much time on HN. If you turn it on you'll only be allowed to visit the site for maxvisit minutes at a time, with gaps of minaway minutes in between. The defaults are 20 and 180, which would let you view the site for 20 minutes at a time, and then not allow you back in for 3 hours. You can override noprocrast if you want, in which case your visit clock starts over at zero.
Thanks for the tip.