Time to hire starts when a specific candidate enters the process, usually when they apply or are sourced, and ends when they accept an offer. It differs from time to fill, which starts when the role opens. If a candidate applies on a Monday and accepts an offer 16 days later, time to hire for that person is 16 days, regardless of how long the vacancy had been open.
Candidates, especially in competitive or hourly markets, often take whichever reasonable offer arrives first, so every extra day carries risk. Long gaps between stages, slow feedback and hard-to-schedule interviews are common causes of delay, and tracking the measure by stage shows where to act. Faster is not automatically better, though: the aim is to remove waiting, not to cut the steps that check whether someone suits the role.