The framerate of the object tracking/pose estimation is around 20FPS, but it also depends on the depth mode used, and the camera FPS/Resolution. (If it's 15FPS for the camera, it won't be more for the object detection).
The precision of the distance is directly linked to the precision of the depth measurement:
At 1 meter, you can reach a precision of few centimeters (<5%)
At 20 meters, the distance precision is 10% therefore around 2 meters (19m - 21m)