You can use something like this:
But add it as a cron job instead of running it in /rw/config/rc.local
.
You can change the system timezone in the cron job as well.
Do you want to use VPN in the sys-vpn or in the qube where you’ll be using apps e.g. browser/messenger/etc?
If you want to use VPN in sys-vpn this way then it’s hard to configure the timezone in the qubes connected to sys-vpn properly.
Also are you sure you want to do this? I’m not sure if this will give you any benefit, e.g. if you’ll be connected to the web server and then your connection will be suddenly changed. You’ll be tracked this way then.