How to manage/limit the Internet-Time of my children with vouchers?

[mispecht]

Hi,
some weeks ago i switched from m0n0wall to OPNsense and I'm very happy with it!
Thanks to all developers!

Now I want to use the vouchers to limit the Internet-Time of my children. But i want limit only specific protocols and/or URLs. Also idon't want to block the Traffic in the LAN. So the normal Captive Portal is not right solution for my requirements.
I tried to use the Voucher Server as an Authentication method for the Proxy Server: I can select and apply it, but it doesn't work. I think this is because it is not possible to grant the voucher user the Proxy-Right.

Do anyone have an idea how to solve this? Or is there another solution for my requirements?

One additional question: Is it possible to create vouchers with only 30 minutes or 1 hour? Actual the smallest value is 4 hours.

Thanks for your ideas and answers
Michael

OPNsense 16.7-amd64
FreeBSD 10.3-RELEASE-p5
OpenSSL 1.0.2h 3 May 2016