I remember having to clean out the ball thing every few days. And if you waited too long, I needed tweezers to scrape the lint loose. I don't recall ever actually needing to clean the optical sensor on an optical mouse.
You shouldn’t need to do it every few days unless your surfaces were particularly grimy. And on those kind of surfaces the slip pads would still need cleaning even on optical mice plus the sensors on the early ones didn’t work too great unless you had clean smooth surfaces anyway. So like for like, ball mice should last 6 months before needing a clean.