Points are valid for one year and drop out automatically day by day (exception are european and world championships – these tournaments stay in 2 years till the next event). You find the point distribution document HERE if you wanna know more about how much ranking point you get for which position.
From the 1st January 2016 players that cant play their own category due to the
low number of players will play any other category that they are allowed to play, but points will
be awarded for all categories that they could play, including their own category.