Midnight at the start of dateString in timeZone, as a UTC instant (e.g. "2026-03-05" in America/New_York → "2026-03-05T05:00:00.000Z").
dateString
timeZone
Midnight at the start of
dateStringintimeZone, as a UTC instant (e.g. "2026-03-05" in America/New_York → "2026-03-05T05:00:00.000Z").