As per Greg's link.
Every 12 months or 1000, 4000, 8000 and every 4000 thereafter. Oil change happens at 1000, 8000, 16000 but the valves needs to be checked every service. Most leave it be.
Have fun looking for the right oil. I haven't found it and the Honda dealers don't have them in stock and don't appear to 1) use the right JASO MB oil at their workshop and 2) no one seemed to have bought any over the counter either.