Subsequent calls to qSetMessagePattern with different %{time ...} values will not change the time format in the debug output.
This happens because the timeArgs list is not cleared alongside literals and tokens in QMessagePattern::setPattern.

For example:

void foo() {
qSetMessagePattern("%{time yyyy} %{message}");
qDebug() << "NARF";
qSetMessagePattern("%{time yy} %{message}");
qDebug() << "ZORT";
}

Will produce:

2016 NARF
2016 ZORT

Instead of:

2016 NARF
16 ZORT