How accurate is google gps location?
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.