@flypig and @chriadam , this is my attempt to patch QTBUG 26161 in 5.6. I'm just adding the missing lines from https://code.woboq.org/qt5/qtbase/src/corelib/time/qdatetime.cpp.html#_ZNK9QDateTime8toStringEN2Qt10DateFormatE and adjusting them to use conventions back from 5.6 version.

I'm currently testing it, but compilation may take a while, so it's still WIP at the moment.