The timing score is not a quality score for the account. It answers one question: is this posting schedule regular enough, spread enough and concentrated enough in its own good slots that timing is not costing reach. Cadence, gap consistency, how many days and hours of the week are used, and how many of the top slots hold enough posts to be worth acting on all feed it.
Every central figure on the page is a median, never an average. One post that escapes into a large feed can be fifty times an account’s normal engagement, which moves a mean by an order of magnitude and a median barely at all. A mean-based chart would mostly report which day of the week happened to contain the outlier.
The timezone estimate is offered only above 20 posts, and only when the account actually has a quiet window. An account that posts evenly around the clock is told there is no timezone to infer rather than handed a confident guess, because that pattern usually means a scheduler or a shared account rather than a person in a particular place.