What, not monthly!?
I don't know of I can look up to you anymore...
When you have the right kind of grinder, it only requires major lubing annually. Since complete burr cleaning takes 10 seconds (if you dawdle), the gearbox only requires cleaning and lubing one a year. And since it is totally isolated from any grinds...it was so clean, I could have waited another year.
In short, once a year constitutes compulsive cleanliness!