So basically you are admitting that Gen 5 does work differently than Gen 3 because something using data in my system was not an issue at all under Gen 3. Never. Now apparently it is. That's something Hughes is doing, not me.
It "works differently" in that it provides faster speed. This means that, for any particular time online, you can use more data with Gen5 than with Gen3 when it comes to things that use data perpetually, like some ads.
The bottom line is this: without a program to monitor the internet data your computer uses you have no way to know for sure. This is what Glasswire does.
So how long do I run Glasswire? It obviously can't look back in time.
As long as it takes. It uses no data, so there's no reason you can't leave it on your system permanently.
A couple of other Windows things that can use data are Syncing and Delivery Optimization. I'd check to see if they're on, and if they are, but you don't have need for them, turn them off. Your browser may also be syncing, and it's the same with that, as in you can turn the browser syncing off if you don't need it.
With Glasswire, make sure to set the options as shown below so that when viewing the results you only see the internet data the computer is using rather than including data that's being transferred back and forth in the computer itself.
You can also ignore the firewall settings. Glasswire isn't a firewall itself, it just gives access to Windows' built in firewall, but it doesn't change anything unless the user does so themselves.