Opening the Modems SCC at 192.168.0.1 will quickly tell you if you have a 7000s or a 9000.
Here is the modem main page for a 7000. Note references to a 7000 on the page:
The unmetered period for a 7000s system has always been based on eastern time regardless of the users local time zone except for users in Alaska. They have recently been changed to local.
They were fiddling with it recently so I guess we will need the Mods to confirm.
9000 systems have always had the legacy daily plans unmetered from 2am to 7am local and monthly plans have the Bonus Bytes period from 2am to 8am local.
Sadly Glasswire is not going to be compatible with his Mac.
Glasswire has threatened to have a version available hopefully in January.
That being the case I can only suggest a change in routers that will allow tracking of usage by device IP.
I use an Asus RT-AC3100:
There are other models that have the "Traffic Analyzer" feature available.