Restricting Site (e.g. youtube) Access time to entire VLAN`

Hi 

I am using XG-115 as my firewall and already got number of rules. I also have a couple of VLANs.

I followed the below guidance given by Sophos tech support team.

The rule works well with individual hosts. but when I replace the individual host with VLANs the rule fails to restrict access

Existing rule 

1. Create a firewall rule at top with source network as VLAN IP address and destination network as any
   1. In web policy create a new policy to block streaming media and YouTube.
   2. Same with application filter create an application filter to block YouTube and streaming media
   3. Create a link NAT firewall rule with SNAT as MASQ
2. Create a firewall rule at top with source network as VLAN IP address and destination network as any
   1. In During schedule time add time frame on which you wan to allow website to get access. 
   2. Create a link NAT firewall rule with SNAT as MASQ
   3. In web policy of firewall select web policy with allowed traffic for YouTube.
   4. In other security feature->identify and control application->select application filter with allowed YouTube

Any guidance is highly appreciated.