A daily meeting must remain at 09:00 in America/New_York. Why is adding 86,400,000 millis…

A daily meeting must remain at 09:00 in America/New_York. Why is adding 86,400,000 milliseconds insufficient?

1. It adds an elapsed 24 hours, which can land at a different local hour across a daylight-saving transition.
2. Date stores timestamps in seconds, so the constant uses the wrong unit.
3. UTC days always contain either 23 or 25 hours.
4. Intl.DateTimeFormat changes the underlying Date when it formats it.