How accurate is google gps location? How accuate is location data using gps? 

My partner went to visit his young daughter at her mother's house, he says he stayed there for 30-40 mins. However, his gps location showed him going to the house, staying there for less than 10 minutes, and then leaving. By pressing the locate button on the device manager I could see the gps recorded location moving in real time. (With his permission to do this btw, his daughter's mother is still in love with him and has no respect for our relationship or our family.)
This matters to me because she wanted him to take her somewhere, but he said he is just going to see his daughter and not running around after her taking her where she wants to go.

So how likely is it that he stayed at her house for 30-40 mins when gps location shows him going up the road, being at the house for around 5 mins and then going back down the road.

I know it can be a bit out because when we are home, it shows a small, dark circle and our house is not within that circle but across the street.

Edit: no its a different issue because he definately was at the location (her house).

The issue is that he says he stayed at the location for 30-40 mins before going on to his next destination and the gps data says otherwise. It says he was there for 4-5 mins and then went to his next destination, which is about 30 minutes away from her house and all the time the location was quite specific, only a couple of cars length and width. So if he really stayed at her house for 30-40 mins then the gps was tracking him going to his next destination when he was still at her house which seems unlikely.
In my personal experience, it's pretty darn accurate. I use Google Location History to help track my time sheets, and I can easily see the exact time I walked out the door at my client and got in my car and drove to lunch, and then from there to my next client, and so on. I'd say the worst it could be is a minute or two off.

The only time I've seen it wildly inaccurate is when I had my tablet also reporting location services from home. Then I saw constant spikes between the two locations throughout the entire day until I disabled it.