Blocking internet to all of the LAN users for a time period using parental control

I have prepared my OpenWRT router to work as a VPN Client device to fight against the Internet censorship,
So my router should perform as follows,
(-1-) Blocking any unprotected (not vpn tunneled) traffic to pass through the ISP,
or better to say enforcing all the LAN devices to use the secure 3rd party VPN traffic.
As soon as VPN tunnels dies the LAN users cannot access to the internet via WAN (kill-switch is accomplished).

(-2-) Executing VPN tunnel performance test for different OpenVPN server sites (locations) and
recording the Download/Upload and Jitter performance of different server sites (locations) at
certain time interval (every Friday at 23:00-23:40).

Having that said I have successfully accomplished part (-1-) but when I am going to evaluate the performance of the VPN Tunnel(s) I should make sure that under the defined test time interval all the LAN devices are blocked from the internet which is provided by the 3rd party VPN provider.

As soon as the LAN users are blocked from the internet the OpenWRT router should execute internally the scripts a couple of times for different OpenVPN tunnels under the mentioned time period and collect the results.
Once the time period is over the blocking Firewall rule should either get deleted, expired or disabled.
(deletion is prefered method)

Please note that I have created a firwall Zone for my OpenVPN to act as a kill-switch and the LAN traffic forwarded to the OpenVPN zone is as follows.

I have tried to create two simple firewall rules under the section traffic rules based on parental control tutorial for blocking the
LAN traffic to passthrough the OpenVPN zone and vice versa but none of them work, and still the LAN users can access to the internet via VPN Tunnel.

I will be happy to get a hint on solving this issue which is really appreciated.