@Carl 

in response to question:  "if more than one device was bieng used at the time?"

No

@Carl 

I have more information that allows me to understand the time accumulation better.

1) Yesterday, my son's xBox accumulated almost an hour of time on it's own before it was ever turned on.  It is hard wired via ethernet.  We were out of the house just about all day, and I checked the insights before we got back home.  My expectations were to see 0 minutes for the insights, but had 58.  It's worth mentioning that the xBox was powered off, but also it is a hard wired device.  And as I understand hard wired devices...  they are never off.

2) Yesterday, my daughter's Nintendo Switch accumulated 37 minutes of time on it's own before it was ever played with.  It is a wireless device.  We were out of the house just about all day, and I checked the insights before we got back home.  My expectations were to see 0 minutes for the insights, but had 37.  It's worth mentioning that the Switch was in sleep mode.  It was NOT off.  I assume if it were off, it would have accumulated 0 minutes.

My conclusion:  Time controls are not linked to the user's activity on a device.  Time controls are linked to the devices activity regardless if a user is involved or not.  Which kinda stinks considering the parental controls parents want to impose.  We tell our kids 3 hours, they see the clock and can do simple math.

John

@jcdean518 

I have found that if my son leaves his Android tablet and his phone powered on they use time even when he is not using them.

Once I explained that all internet devices use time when on, he shut them off when not in use, and his 3 hours lasted close to 3 hours.