When may the masthead light or all-round white light on a power-driven vessel of less than 12m be displaced from the fore and aft centerline of the vessel?

The masthead light and all-round white light on a power-driven vessel of less than 12 meters may be displaced from the fore and aft centerline of the vessel at any time. This flexibility is provided in the COLREGs to accommodate operational needs without compromising safety or compliance with navigational rules.

For vessels that are less than 12 meters, the regulations offer some leniency regarding the positioning of lights, recognizing that smaller vessels may have varied designs and operational practices. By allowing the lights to be positioned away from the centerline at any time, this rule enables better visibility and functionality depending on the vessel's activities, configurations, and requirements at any given moment.

The other circumstances outlined in the options pertain to specific situations where the visibility of navigation lights is crucial, but they do not limit the general rule that permits light displacement at all times for smaller vessels. Thus, the answer emphasizes the operational versatility permitted under the regulations, ensuring proper signaling and safety can be maintained in various conditions.