Okay so suprisingly there is no standard way to get Docker to automatically pick up correct timezone from the machine, but if you know the timezone you use then its quite easy to pass it to the Docker container
On Synology, you need to add variable TZ to the timezone, this usually has a value of the form Continent/City
So for example here I change it to Europe/London, during Winter London timezone is the same as UTC but in Summer it uses British Summer Time which is one hour different so setting the timezone sets the time correctly.
You say you are eight hours ahead of UTC , so setting it to Australia/Perth should work for you ( I tried it out).
A full list can be found at https://en.wikipedia.org/wiki/List_of_tz_database_time_zones
I assume Qnap and Unraid are similar.