QDateTime should support RFC-3339 formatted timestamp with nanosecond precision.  Computer runs a lot faster these days than a decade ago.   Millisecond precision is not enough anymore.   I checked QDateTime source code.  Looks like it will be a minor change.  Update the parsing in fromIsoTimeString function.  Use double instead of float to store the second with ns.   It would be nice to have this small feature added in 6.2 release.