Blocking Roblox

Hello Everyon,

I have created a profile for my son on my network and have limited his access to the internet for 2 hours a day, but when his device is connected to the internet he plays Roblox and this continues until someone manually disconnects his device from the network by turning off the wifi on his device otherwise he keeps playing and the internet access is not stopped to his Roblox. To be specific and make it short, once the 2 hours limit is met his Roblox still has an internet connection and he keeps playing until I realize it and manually disconnect him. Is it a bug with the firewall or something else?

Thank you,