Hi Vipul,
Thanx to answer back.
I don’t really know if it works or not by creating TIMEZONE. First, I created an environment variable as mentionned in the doc (not sure to remember). Anyway, it wasn’t what I expected.
I thought it changed my logs with the right timezone and something happenned because services stopped and automatically restarted. UTC switch turned to grayed and off and TimeStamps too but the good (for me) was reading as variable I guess.!
I tried TZ too as you can see in the picture below (override means or depends if I did it sometimes in DEVICE VARIABLES or sometimes in Application ENVIRONMENT VARIABLES, I guess…not sure too).
I don’t know exactly what behavior I had to expect. I was wrong, I thought it was a way to change in each docker/service/container ?! Probably silly to expect that! 
I tried to change directly with command line and prompt terminal in HostOS to understand better what I’m allow to do…
I finally tried to change in right place srly-ose-viewer because, I want to display the right time in France in front of webbrowser (HDMI ouput). By pushing balena-timezone here, i was avable to set Europe/Paris timezone (only UTC was able before), I set by the command sudo dpkg-reconfigure tzdata and after launching start.sh I saw everything goes fine like I want. And get what I expected in front user HDMI display.
I’m really sorry I’m a real newbie and discovering Python, Balena, RaspberryPi etc… It’s a new world for me, I hope I gave you a clear answer to your question - probably not 
I started my project few days ago and I have to learn everything!!! Thanx for the link by the way and forgive my VERY BAD English…
Let us know if this works out for you. Also, please do let us know where else the TIMEZONE env var has been referenced and help us update that both on our side and the Screenly OSE project. Thanks!
I read a lot those last few days to launch my project, not really sure about my sources.
i correct myself because of this Viewing/Setting Timezone - Balena - Anthias Forum
The timezone thing came fromt that GitHub - balena-io-examples/balena-timezone: Example of how to set the timezone within a container
I didn’t understand yet that Time management - Balena Documentation
Chrony seems great but too complicated to me for now
I do not wish to take up too much of your time but do you know if someone in Balena Team could answer to my Cron question??
Here —> CRON tasks question : Newb tries to launch simple project RPi4+BalenaOS/Cloud+Screenly
Thank you very much.