Quote Whonix ™ Post Install Advice:
To protect against time zone leaks, the system clock inside Whonix ™ is set to UTC. This means it may be a few hours before or ahead of your host system clock. Do not change this setting!
Change System Timezone
Whonix ™ unspecific part: Time zone can be adjusted as per Free Support Principle.
Note: system timezone as configured
/etc/localtime is a "system setting". What (Xfce) graphical user interface clock widget is showing and its setting might be independent from the "system setting" since that is a "user setting".
Timezone vs sdwdate
sdwdate is mostly unrelated. It can operate independently of system timezone setting. It is a time synchronization daemon. It does not alter the system timezone.
Footnotes / References
sudo mkdir -p /usr/local/etc/sudo touch /usr/local/etc/noutc