I may have suggested this a couple years back but thought I might suggest again.
There was a feature I used a long time ago, I think it was dd-wrt on a 54gl router that would introduce latency to some devices at a certain time. It wasn't in the gui, but a script. Why you might ask? Its real handy as a parental controls to reduce pvp gaming if you use it with a a set time, like add 2000ms from 1am to 7am. This could be added to the 'shaper' section in firewall. I think this can be done in feebsd with a package called dummynet and in linux with tc. There is probably close to 0% interest in this feature but if its easy to add, why not.
Oh that's sneaky }:->
I think the capability is already present. You can create a Pipe in Firewall->Shaper with a packet delay (under Advanced settings). Example of that in this thread (https://forum.opnsense.org/index.php?topic=37413.0).
Then you can create a schedule in Firewall->Settings->Schedules.
Finally you can add an interface rule and apply the schedule within it. There's a new/experimental feature in OPNsense which lets you apply the shaping in the pf rule itself (by selecting the pipe).
Haven't tried this but I think it should work. The only thing I'm not clear on is how to prevent the pipe from reducing the total available bandwidth for other clients because this is essentially bandwidth reservation. You might have to narrowly define the pipe bandwidth for the specific client you want to throttle and just accept the loss of that bandwidth, but I might be mistaken about this.
The shaper is basically using dummynet/ipfw.
As suggested above you can play with the delay parameter to obtain the requested result. However to me it looks bit pointless as you can have a time schedule on FW rules. Just create permit or deny rules for your kids Networks at the time desired and you are done.
Regards,
S.
The way I interpret this, OP wants to give the impression to the child that the internet and/or game server becomes unusable at night without making it too obvious that parental control has taken place. :)
Well but the same is clear as well when the game servers stop to work yet Kids can browse the internet :D
My suggestion was in mind, that in my professional opinion, is better to have the game down than have lags.
Lags make gamers more crazy.
Regards,
S.