I am the account owner, and I am wondering if there is a way to obtain detailed records [spanning approximately 1-2 months] of when an individual device connected/disconnected? The daily usage is very helpful; however, this information is only available for a 24-hour duration, and the 7-day view merely provides the amount of time connected, not the time/hour during which an individual device connected/disconnected.
Would I be able to contact Comcast/Xfinity cusomter service to get these records?
Comcast should not be able to see individual devices behind your NAT firewall. The router or Xfinity gateway might be able to track data by specific device, but I don't know of any that do.
I did have an AC capable gateway some time ago and it did not have per-device usage that I could find.
Some third party routers do offer per-device data usage, such as some from ASUS, but I am not sure exactly which ones.
Here is an example: https://www.wirelesshack.org/routers-that-can-monitor-data-bandwidth-usage.html