The option to do this via your Hub is not currently available. However I think that Child Safe will be a good option for you.
With Child Safe you can set date/time preferences and block, or make exempt, specific sites. Please give it a try and let us know how you get and welcome to our Forum, thanks for joining
The issue with child safe is it won't let you block PC games, CS:GO uses community servers and even if you block access to the main steam master servers you can still very easily just have the game connect directly to any game servers as those are hosted by 3rd parties, it won't actually serve any purpose in this instance, you would need a router with more complex white/blacklisting features than the stuff virgin supplies, this will cost you money and VM won't be able to help you with setup of the new router much, if you didn't want your child playing CS:GO why did you let them buy it in the first place?