MBlume may be referring to the "noprocrast" feature:

the latest version of Hacker News has a feature to let you limit your use of the site. There are three new fields in your profile, noprocrast, maxvisit, and minaway. (You can edit your profile by clicking on your username.) Noprocrast is turned off by default. If you turn it on by setting it to "yes," 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.

Best wishes, the Less Wrong Reference Desk.