Corporation/Threat Clocks and the Reporters' Noise and Story Clocks are the only clocks that have rules about how they are created. (Those are really special rules about the Links phase and the Reporter playbook rather than about the clocks, but I probably need to explain this better in the text.)
All other clocks exist prior to the first advance and are simply advanced.
Once a clock exists, it takes six advances to fill it:
1 (to 1500)
2 (to 1800)
3 (to 2100)
4 (to 2200)
5 (to 2300)
6 (to 0000)
Does that clarify it?