The tasks:OrdinalDate element is an optional child element of the Flag element (section 22.214.171.124) that identifies the time at which the client set the flag. It is defined as an element in the Tasks namespace.
The value of this element is a dateTime data type, as specified in [MS-ASDTYPE] section 2.3.
A maximum of one tasks:OrdinalDate child element is allowed per Flag element. The result of including more than one tasks:OrdinalDate child element per Flag element is undefined. The server MAY return a protocol status error in response to such a command request.