When should a dead reckoning position be plotted after obtaining a fix?

A dead reckoning position should be plotted after obtaining a fix to maintain a continuous and accurate navigation record. Once you have a fix—which is a precise determination of your vessel's position—you can then calculate your movement based on the course and speed for a specific period. This method relies on the last known accurate position, hence allowing you to project your current position based on input data from previous movements.

When you obtain a single line of position, it is often not enough to establish a definitive fix, as it represents a potential location along that line, not an exact point. However, once you have a reliable fix, you can indeed begin plotting your dead reckoning positions as you proceed, making it essential to do this to maintain navigational accuracy and situational awareness. This practice ensures that your navigational data reflects changes as you make progress towards your destination.

Other options suggest either unnecessary waiting periods or conditions (like only plotting during daylight) that do not align with standard navigation practices. Dead reckoning relies on constant tracking and updating to ensure safety and efficiency in navigation rather than arbitrary time constraints or visibility factors.