I think you missed the point.
If I have 1 observer, he cannot measure distance just using a clock. All he can do is time events. That's not measuring distance.
If the there are 2 observers, and they both see the same events, then they can time events, and one observer can tell the other one...
Suppose that we do not have any way to measure distance, but do have clocks. There are N observers, who can all see the distant events, say spaceships taking off and landing on far away planets. The question is: assuming the speed of light is constant, can we deduce the distance to the events...