Yes, it is a
personal use day even if you did not stay there overnight. In your scenario, your personal use days
would be 330.
You are still “using” the apartment as your personal residence during the time you are
absent by leaving your belongings behind.
If you were dealing with a property that is more like a hotel or a vacation rental (instead of a personal residence) in that
when you leave you take everything with you, then you would not have a personal
use day when the property was vacant and not used by either you or another renter.
