'local times'

Early navigation was subject to the limitations of supplies and power. Ships carried enough supplies to reach their destinations, sailing under normal conditions. But early navigation was crude. Latitude could be estimated by the position of the sun’s arc. It would be low in the sky at the poles and overhead at the equator. The time-zones that span the oceans could reflect longitude if ships could keep the times of the home ports. Ships sailing out of Greenwich could use their instruments to determine when it was noon at sea (based on the azimuth) but not what time it was in Greenwich.
If ships had a sea-worthy clock it could tell them how many hours and minutes they were off ‘the mean’. They could then chart and avoid/find geographic features at sea. But swells and other elements can be hard on clocks. So, before on-board clocks they had to subscribe to a lot of ‘guess work’ instead. ‘Lost at Sea’ is the story of a self-taught clockmaker that set-out to solve the problem by creating an on-board clock that would hold-up to the conditions at sea.
Every hour ahead/behind the time in their home ports represents 15 degrees. At twelve hours ‘off the mean’ a ship would be equal distance east or west (180 degrees) from where it had set sail. Like a British ship out of Greenwich would be in New Zealand. Cape Horn would be about ¼ of a day behind the mean and ¾ of a day behind the International Date Line. The cape of Good Hope isn’t far off the Greenwich mean. Ships lost at sea in the vast waters of the Indian and Pacific oceans could find their way to more familiar waters if they knew which waters they were closer-to.
Once it was proven successful it was widely adopted. The same method of navigation in ‘minutes’ is still used in modern on-board navigation systems. It can be done with sophisticated GPS systems or more simply with a good timepiece and a bearing. You need to keep track of mean and local times (and which hemisphere you are local to). It is a fairly young technique. It has only been in practice for the last 500 years or so since a sea-worthy clock was developed. But it might be one of the most significant advancements of the common-age. Thanks to the British Empire’s maritime interest in developing an accvrate global positioning system.