How could I monitor how much time my kid plays with fortnite?
What is “Minotor” on the title? Minotaur?
Easy: They will play it every single moment you don’t control it.
There are two things:
Or you let your kid educate you on his habits,
or educate your kid properly, so that he respects what you tell him.
Promise him that the first time you catch him using the game beyond what you allow him to do,
you’ll broke it all over and he’ll never use it again until he do not live on his own.
Do this and it won’t be words thrown away when you talk to him… You will have his complete attention.
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Usually some games have “how many hours have you played”, so check that info on game profile.
If when you leave the profile says 1 year 3 months 4 days and 10 hours, and when you come back it says 1 year 3 months 4 days and 22 hours, the calculation is easy…
Why not ask… using words, How many hours have you played fortnite today?
Join steam login and see if player is online 
If you cant beat him join em… Interact with your kids in any way you can.
You can restrict the time-of-day a device (PS5, Xbox, etc.) is allowed to access the network with /ip/kid-control. While that give you usage by device by day, not exactly what you’re looking for however. Finding application in a network flow just isn’t easy…so identify specifically Fortnite be very difficult & at best in-exact.
You can also run dude which at least give you a chart of any usage over time for a device. Now Dude also wouldn’t help with specifically finding Fortnite.
Oh you mean being a parent is harder than configuring MT ROS LOL… No sheite.
So you’re saying there is no wan to measure it with the router… sad.
This just is not a feature of network router. Is it suppose to identify Mario Kart or Doom too?
You can restrict a device (say Xbox, PS3, etc) by time-of-day. It’s that you want to restrict by application that makes this problematic. But, RouterOS is very flexible, so if you want to research what network IP/ports it uses, you can do something. But the issue is modern games use a variety of NAT traversal methods, so it just not easy to find specific application. This isn’t “sad” — it just how networks and routers work.
Assuming you know the IP/ports/etc that make up “Fortnite traffic” (and that’s a big IF since other games may use same ports and/or Fortnite uses many domains/IPs…)… the “in time” part of the request here can be solved with /ip/kid-control or some network monitoring tool (like Dude or third-party).