The PMDesignator property is used for all times from 12:00:00 (noon) to 23:59:59.999.
If the custom pattern includes the format pattern "tt" and the time is after noon, DateTime::ToString displays the value of PMDesignator in place of the "tt" in the format pattern. If the custom pattern includes the format pattern "t", only the first character of PMDesignator is displayed. Your application should use "tt" for languages for which it is necessary to maintain the distinction between AM and PM. An example is Japanese, for which the AM and PM designators differ in the second character instead of the first character.
For cultures that do not use a PM designator, this property returns an empty string.
Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)