There are lots of different types and brands of bait stations on the market. They can differ greatly in their style, size, internal components, active ingredients, and manufacturer recommendations. The best way to determine the recommended interval between station checks and monitoring is to read the directions that come with your particular stations.
If you are still unsure as to how often to check your stations, the best answer I can give is to check your bait stations as often as you can. The more often you check them, the better off you are. If you check them quarterly, as opposed to someone who only checks their stations once a year, you can greatly reduce the potential for serious damage, should you develop an active termite infestation.
With the particular bait stations that we use, the manufacturer recommends that we monitor them every 3 months, but allow us to check them every 6 months, depending on how they are set up. We choose to monitor them every 3 months. We do so to minimize our risk, and the potential for costly termite damage.