It *is* in the full league rules. The problem is that when @Dean
spiffed up the site with nice links (which we asked for and appreciate) the full rules were not linked in both sets of links. In other words, the links look and are different depending on whether you get to them by clicking on the left or the right on the home page. Dean, please fix when you get a chance.
The rule is that you can claim a forfeit win when the game says "5 days" unless your opponent announced the need for longer time on a specific move (i.e. vacation, work, finals, whatever). That said, we strongly encourage folks to wait longer and PM their opponent on this site and make a comment in game, especially if the game is still equal. If you admit your losing, claiming a win right on the 5 day make is definitely poor sportsmanship.