It depends on your Yorkie, their coat type, skin sensitivities and how much they roll around in the fun stuff outside, lol
My guys are usually every 10 -14 days, in the winter it is longer. I have gone up to 4 weeks with one of them, and she still smelled good
(the luck of the draw)
I think when my Yorkie was a puppy, I never bathed more than every other week, just gently wipes with baby wipes when needed.