Per season or so: spring, summer, fall, winter. If I owned AC and had a more regulated room temperature , probably less.
It is important to use the buttons on the remote by quickly tapping them,* tap, tap, tap*, and not holding them down continually, to achieve the very well designed, small increments the focus mechanism is capable of.
With careful attention you should be able to focus so precisely that even with the unit's clever use of smooth screen technology the individual sub-pixels of red, green, and blue start to be just barely visible.
[I have a good photo of this but for some reason AVS or Flickr isn't allowing me to link to my Flickr account. Seems only Flickr members are allowed to view stuff anymore, perhaps.]
In A/V reproduction accuracy, there IS no concept of "accounting for personal taste/preference". As art consumers we don't "pick" the level of bass, nor the tint/brightness of a scene's sky, any more than we pick the ending of a novel or Mona Lisa's type of smile. "High fidelity" means "high truthfulness", faithful to the original artist's intent: an unmodified, neutral, accurate copy of the original master, ideally being exact and with no discernable alterations, aka "transparency".