ISO8601 spec allows for capturing time down to microseconds (0.000001) - that is 6 digits after decimal point. While current RM ISO8601_TIME Class defines Real type to capture fractional seconds there's potentially conflicting information which depicts: hh:mm:ss[,sss][Z | ±hh[mm]] (Note 3 fractional digits which can only cater for milliseconds)
It seems at least one implementation (Marand) is not saving >3 digits after decimal point so they may have implemented this as a constraint.
I suggest revising these format statements as: hh:mm:ss[,ssssss][Z | ±hh[mm]] And also providing accompanying text to clarify this is not a limitation and values for microseconds (and possibly beyond) should be supported.
Ocean's Archetype Editor also provide microseconds as an option to define Event's periodicity and to define Interval duration but fail to save with Archetype (Hence is a bug).