Methodology
How Hours Apart works
Time-zone answers should be explainable. This page describes what the site calculates, where the underlying rules come from and where you should verify a result elsewhere.
Local time and daylight saving
Hours Apart uses the browser's built-in Intl time-zone support and IANA time-zone names such as Europe/London and America/New_York. That lets a selected date be resolved using the rules for that date, rather than assuming today's offset applies all year. The pages compare offsets across future dates to identify when a gap changes.
City coordinates and daylight
Each city has an approximate latitude. The site uses that latitude and the selected date to estimate sunrise, sunset and the length of daylight. Latitude matters: places in the same time zone can see very different sunrise and sunset times. These values are planning aids, not a substitute for local astronomical or official weather information.
What can change
Governments can change daylight-saving rules, sometimes with little notice. Browser and operating-system updates carry IANA rule updates, and the site is rebuilt as its content is maintained. For a flight, visa deadline, legal filing or other high-stakes commitment, check the relevant authority or provider as well as the planned calendar event.
What the planner does not know
The meeting planner does not read calendars or free/busy data. Its working-hour bands are the hours you choose for each person. It is designed to make a proposed meeting understandable before you send an invite, not to decide availability for you.