You have it a little bit backwards.
You just need 1 for time in the accuracy that a human needs it. 2 will give you a circle on a sphere, 3 one of 2 points on a circle (but one will not be on earth so discarded, 2D fix), and 4 is the minimum for an accurate 3D fix.
The signal from a sattelite is accurate time data from its internal clock. The reciever is just calulating the distance from each sattelite by the difference in the recieved time data and the sattelite position from the almanac (or calculated in the reciever with known or recieved orbit data).
Edit: found this
https://wiki.openstreetmap.org/wiki/...cy_of_GPS_data