I had a TZ en variable set to GMT1 (my coworker didn't have said variable) and the time displayed matches the GMT-1. If I set that variable to GMT-2 or remove it I do get the correct GMT+2 time.

That being said while the time in the QDateTime matches that TZ variable the Timezone in the QDateTime doesn't so there might still be an issue there. I'll update my ticket.

It was a guess about TZ. That is a normal environment variable under Linux (which I use) but not so much under Windows. There it gets complicated: it may depend on the compiler code you use (MinGW vs MSVC). I believe it is also used automatically by the C runtime code you link/dynamically load (DLLs) against. How that in turn relates to C++ runtime code I don't know. And I suspect Windows calls do not use it, only C/C++; and then I don't know which Qt calls' implementations use C/C++ functions versus Windows-SDK ones, and maybe a mixture (e.g. your time calculation calls use the C/C++ TZ variable but your name-of-timezone uses a Windows call?). And for all I know Qt's internal code may have changed in that area between your old-working Qt5 and new-non-working Qt6. It's all perhaps a minefield, suck it and see :)

I had a TZ en variable set to GMT1 (my coworker didn't have said variable) and the time displayed matches the GMT-1. If I set that variable to GMT-2 or remove it I do get the correct GMT+2 time.

That being said while the time in the QDateTime matches that TZ variable the Timezone in the QDateTime doesn't so there might still be an issue there. I'll update my ticket.

• Does your machine/user have any TZ environment variable set?
• Does your Registry have HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation and is it same as other users?

• Added QCoreApplication instanciation
• Updated Qt version (same result with Qt 6.11.2 and 6.12.0 rc)

From what I see now:

• Systemtime is correct UTC
• LocalTime is my OS displayed time
• When getting a currentDateTime from a timezone build with Qt::localTime the timezones seem to be different but I'm getting the same time
• When getting a currentDateTime from a timeZone build with systemTimezone the timezones seem to be equal but I'm getting a different time

I'm going to open a ticket but since the issue is only happening on my machine I think there must be something weird somewhere else 🤔

Btw, I thought initially the lack of QCoreApplication might affect it, but I tried mine with and without and it made no difference (still correct). You might just put one in in case it affects your situation.

From https://codebrowser.dev/qt6/qtbase/src/corelib/time/qdatetime.cpp.html#_ZN9QDateTime15currentDateTimeERK9QTimeZone the definition of QDateTime QDateTime::currentDateTime(const QTimeZone &zone) introduced at Qt 6.5 reads:

QDateTime QDateTime::currentDateTime(const QTimeZone &zone)
{
    return fromMSecsSinceEpoch(currentMSecsSinceEpoch(), zone);
}

while the overload without parameter is:

QDateTime QDateTime::currentDateTime()
{
    return currentDateTime(QTimeZone::LocalTime);
}

Knowing this you might want to investigate a bit further why they are giving you different results in your environment and find where the underlying odd behaviour is coming from.

int main(int argc, char** argv)
{
    QCoreApplication app(argc, argv);
    qDebug() << QDateTime::currentDateTime().timeZone();
    qDebug() << QDateTime::currentDateTime().toString("dd/MM/yyyy hh:mm:ss");
    qDebug() << QTimeZone::systemTimeZone();
    qDebug() << QDateTime::currentDateTime(QTimeZone::systemTimeZone()).toString("dd/MM/yyyy hh:mm:ss");
    return 0;
}
QTimeZone("Europe/Berlin")
"25/09/2026 10:37:14"
QTimeZone("Europe/Berlin")
"25/09/2026 10:37:14"