Yeah, exactly. When there's only a need for time of day then the time is enough. The standard lets you pick the tool you need here, it's not going to have some

Yeah, exactly. When there's only a need for time of day then the time is enough. The standard lets you pick the tool you need here, it's not going to have some kind of procedure for determining whether your application should use one thing or not. It's very clear that here that undesignated time stamps are the wrong one. The standard only describes a set of tools, what I said was common sense.However, the information is there. In 5.3.4.1 you have "When it is required to indicate the difference between local time and UTC". When it is required. If your time zone changes it obviously is required.