Plex: Limit to Airing Time - Always an hour off

I had an issue with Plex where the limit to airing time shown in the drop-down was an hour out, to fix this I had to upgrade to the latest version of Plex as this is a bug, and also I had to fix my system clock on the server.

See this issue for some more info: https://forums.plex.tv/t/limit-to-airing-time-always-an-hour-off/553640

This is how to set your clock to a time zone.

# show the time, was hour out.
sudo hwclock --show

# list time zones
timedatectl list-timezones

# set time zone
sudo timedatectl set-timezone Europe/London
sudo timedatectl set-ntp on

# show clock check its correct now!
sudo hwclock --show

Once this was done it started working.