When you need to. I know that’s vague but no one out here can really tell you. But here is a starting point. First, check for pad wear. If the pads are worn too much or worn unevenly, replace them. Uneven wear indicates a problem between the caliper and pads. Then squeeze the brake pedal against the front nerf bar. The pedal should not touch the nerf and should not creep forward as you maintain pressure. Now bleed the brakes and test the pedal travel again. Use ONLY the brake fluid approved for your brake system. When the pedal starts to travel more or the pedal does not seen as firm, bleed again.
We come from road racing a Sn Rotax and I bleed ours before every race weekend and checked the pedal travel several times during the weekend.
Be safe and have fun.
Thanks for the info Tony. I find I am having to bleed them every race/practice. I swapped out the seals this off season so I was hoping that would reduce the need but even with it sitting for a week or two they still need bleeding.