This has two meanings depending upon its application.
Lookout - When applied to Lookout, Clock Code is a method of identifying an azimuth direction from the aircraft. Directions from the aircraft begin from 12 O’clock being directly ahead with 6 O’clock being directly astern.
E.g. 4 O’clock indicates a direction past the abeam on the right side of the aircraft.
Drift - When applied to Drift, Clock Code is a method of mental arithmetic to estimate the Sin() function. The difference between the wind direction and the aircraft‘s flight path is compared to minutes of a clock. The resulting potion of the hour is the portion of Max Drift to be used to estimate the angular correction to make to offset the aircraft‘s heading and so allow for drift, thus keeping the aircraft on track.
E.g. 30˚ implies 30 minutes which is half an hour and so half the Max Drift should be applied towards the wind for the aircraft to maintain the desired track.