On break in (dino) 500, 1200, (synth) 2000, 4000 then from there it depends on how hard it is ridden. The transmission actually lets you know when you should change it. I notice a difference when I shift. As soon as I start to feel it I change the oil. This usualy comes between 3500-4000. If it starts earlier, I change it earlier. It's better to change it earlier, if you think something feels different than not and pay a higher price later.
Later,
Steve