The default release is midnight for each region. In the United States, this is specifically 9:00pm PST / 12:00am EST.
Timed-release is when the release goes live all at once, so a timed-release at 12:00am EST (New York time) goes live in London at the same time - 5:00am (London time).
Note: Timed releases are best used for exclusive radio or video premieres that are aligned with a marketing timeline usually with a marketing partner. Otherwise, it its recommended to use the typical release date timing which goes live at 12:00AM local time.