interval.round()

interval.round(date)

Returns a new date representing the closest interval boundary date to date. For example, timeDay.round(date) typically returns 12:00 AM local time on the given date if it is on or before noon, and 12:00 AM of the following day if it is after noon.

This method is idempotent: if the specified date is already rounded to the current interval, a new date with an identical time is returned.