@chDVRuser If on your Synology you run:
docker info 2>/dev/null | grep Kernel
what do you get? I'm thinking about querying the docker host to get that value, as I believe it would be pretty good for offering suggestions for several OS-specific things.
On Windows, it looks like this:
Kernel Version: 5.15.167.4-microsoft-standard-WSL2
@chDVRuser Also, it appears it's OK to have comments in with your Poratiner env vars. I'll test it more tomorrow, but if it holds true with the testing I've done, I could add OS specific comments to certain values. Like the need to create a directory on Synology first before deploying, or the limited writable paths on Mac Docker hosts.
My older Synology NAS
# docker info
Server:
Server Version: 20.10.3
Kernel Version: 3.10.108
Portainer Host Details
Kernel Version 3.10.108
Engine Details
Version 20.10.3 (API: 1.41)
My newer Synology NAS
# docker info
Server:
Server Version: 24.0.2
Kernel Version: 4.4.302+
Portainer Host Details
Kernel Version 4.4.302+
Engine Details
Version 24.0.2 (API: 1.43)
Much better than reading comments in the compose statement and having to find the env vars below in Portainer!
FYI
Fails to create container on Synology. No host link or file named /etc/timezone
- /etc/timezone:/etc/timezone # fails on Synology
had to modify this for it to work on Synology NAS
- /etc/TZ:/etc/timezone:ro # works on Synology
OR use this
- /etc/localtime:/etc/localtime:ro # works on Synology
Rats! None of the options that work on Synology also work on Debian -- so I'll remove that binding. Thanks for checking.
Figures 
I dismissed /etc/localtime because it's a binary. But, I get:
/usr/share/zoneinfo/America/Denver
With:
readlink -f /etc/localtime
Does that work for you?
On my Synology NAS's it's a link
# ls -l /etc | grep time
lrwxrwxrwx 1 root root 34 Oct 11 2022 localtime -> /usr/share/zoneinfo/Canada/Pacific
and /etc/TZ is a file
# ls -l /etc/TZ
-rw-r--r-- 1 root root 23 Oct 11 2022 /etc/TZ
# cat /etc/TZ
PST8PDT,M3.2.0,M11.1.0
Does readlink work?
Just tested on WSL Linux, and it works there too. We might have a winner...
Yes
# readlink localtime
/usr/share/zoneinfo/Canada/Pacific
But there is no link or file named /etc/timezone, only the file TZ and link localtime
I'm inclined to go with it. If it works on Synology, and Debian (which so many other distros are based on) -- it seems like a pretty good bet:
As you suggested:
- /etc/localtime:/etc/localtime:ro
As long as the binding doesn't cause the spin-up to fail, I feel like there's a good chance I can extrapolate the timezone.
I think I need to find out what happened to the now 0 byte file /usr/share/zoneinfo/Canada/Pacific
# ls -l /etc/localtime
lrwxrwxrwx 1 root root 34 Oct 11 2022 /etc/localtime -> /usr/share/zoneinfo/Canada/Pacific
# readlink /etc/localtime
/usr/share/zoneinfo/Canada/Pacific
# ls -l /usr/share/zoneinfo/Canada/Pacific
-rw-r--r-- 2 root root 0 Mar 25 00:55 /usr/share/zoneinfo/Canada/Pacific
# cat /etc/localtime
# cat /usr/share/zoneinfo/Canada/Pacific
# cat /etc/TZ
PST8PDT,M3.2.0,M11.1.0
Don't know what I did, but it's now a 0 byte file
# stat /usr/share/zoneinfo/Canada/Pacific
File: /usr/share/zoneinfo/Canada/Pacific
Size: 0 Blocks: 0 IO Block: 4096 regular empty file
Device: 900h/2304d Inode: 6701 Links: 2
Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2025-02-25 21:41:10.834000162 +0000
Modify: 2025-03-25 00:55:34.318494766 +0000
Change: 2025-03-25 00:55:34.318494766 +0000
Birth: -
Fixed it, I'm in the US, not Canade, so
root@DS1513PLUS:/etc# ls -l | grep time
lrwxrwxrwx 1 root root 34 Oct 11 2022 localtime -> /usr/share/zoneinfo/Canada/Pacific
root@DS1513PLUS:/etc# ln -f -s /usr/share/zoneinfo/US/Pacific localtime
root@DS1513PLUS:/etc# ls -l | grep time
lrwxrwxrwx 1 root root 30 Mar 24 18:42 localtime -> /usr/share/zoneinfo/US/Pacific
Great.
I'm working on the next generation of EZ-Start, which will allow spinning-up OliveTin from the command line, and install CDVR (if not already present) with extensions from there.
I'm hoping to continue to hit you up with the occasional sanity check on old/new Synology compatibility, with the most recent being:
Does this work, and what's the output:
timedatectl show --property=Timezone --value
So far, this works on Debian and derivatives, including WSL2 Linux...
my output on Debian and Ubuntu WSL2 is: America / Los Angeles. I expected to see US / Pacific.
That is what mine is I have never used US/Pacific.
Both Continent/City and Country/Timezone are generally acceptable for most purposes -- for OliveTin either is fine. Continent/City is the more "modern" approach as I recall, but I've always liked Country/Timezone. 
Something about dogs and tricks comes to mind...
The timedatectl utility is not available on either of my Synology NAS's