6. System Date and Time

Set RTC (realtime clock) to UTC, use NTP with timezone.

timedatectl set-local-rtc 0
systemctl enable --now systemd-timesyncd
sudo ln -sf /usr/share/zoneinfo/America/Los_Angeles /etc/localtime

6.1. Windows Dual boot

Dual booting requires Windows 10 to use UTC instead of RTC. Disable the NTP client for windows use manjaro to adjust the clock. See: UTC Realtime Clock.

6.2. Force ISO8601 date/time

Forces YYYY-MM-DD 24H time for KDE lockscreens / clock.

0644 root root /usr/share/plasma/look-and-feel/org.kde.breeze.desktop/contents/components/Clock.qml

// text: Qt.formatTime(timeSource.data["Local"]["DateTime"])
text: Qt.formatTime(timeSource.data["Local"]["DateTime"], "hh:mm:ss")

// text: Qt.formatTime(timeSource.data["Local"]["DateTime"], Qt.DefaultLocaleLongDate)
text: Qt.formatDate(timeSource.data["Local"]["DateTime"], "yyyy-MM-dd")

Reference