A date specifying a day is a Duration. A date that is a truncated/rounded timestamp is the same as the millisecond at the start of that date. 2021-02-27T00:00:

A date specifying a day is a Duration. A date that is a truncated/rounded timestamp is the same as the millisecond at the start of that date. 2021-02-27T00:00:00.000Z === 2021-02-27 if truncating. But the day 2021-02-27, first of all starts and ends at different times, depending on your local timezone, but for me it's (in ISO8601 format) 2021-02-27T00:00:00.000+11/P24H. To cover the whole world, it would be 2021-02-27T00:00+12/2021-02-27T23:59:59-12 or 2021-02-26T12:00Z/2021-02-28T11:59:59Z which is 48 hour duration :)