When was the International dateline first used?

Question

When was the International dateline first used?

Answer 1

*****No "official" International dateline has ever been established, however, time zones have been accepted and are in use.  

"The IDL drawn on the map on this page and all other maps is now and always has been an artificial construct of cartographers—it is de facto. No international organization nor any treaty between nations has fixed the 'straight line' segments and their junctions. All nations unilaterally determine their standard time zones, which are applicable only on land and adjacent territorial waters. These national zones do not extend into international waters. Indeed, the 1884 International Meridian Conference explicitly refused to propose or agree to any time zones, despite 'common knowledge' that they did, stating that they were outside its purview. The conference resolved that the Universal Day (midnight-to-midnight Greenwich Mean Time), which it did agree to, "shall not interfere with the use of local or standard time where desirable."

Answer 2

What appears to be the earliest reference to the circumnavigator’s paradox is found in the works of the Syrian prince and geographer-historian Isma‘il ibn ‘Ali ibn Mahmud ibn Muhammad ibn Taqi ad-Din ‘Umar ibn Shahanshah ibn Ayyub al Malik al Mu’ayyad ‘Imad ad-Din Abu ’l-Fida (1273 - 1331). In his Taqwin al-Buldan (‘The ??? of the Lands’), Abu ’l-Fida described how a traveller, depending on his dircetion of travel, would either lose or gain a day at the completion of his circumnavigation [Rudolf Wolf, Handbuch der Astronomie, Ihrer Geschichte und Literatur (Zurich, 1890), vol 1, pp. 465-466; I still have to check the original source].

Another early reference to the circumnavigator’s paradox is found in the works of the French scholar Nicole Oresme (c. 1325 - 1382). In his Traitié de l’espere (which was also translated into Latin as the Tractatus sperae), Oresme presented a “remarkable circling of the Earth” by two imaginary travellers Jehan and Pierre (Johannes and Petrus in the Latin version) who set out to journey around the world along the equator in opposite directions at a speed of 30 degrees of longitude per 24-hour day. Jehan, travelling in a westward direction, would claim at the completion of his journey that it took him only eleven days and nights while Pierre, travelling in an eastward direction, maintained that it lasted thirteen days and nights. A third man, Robert, who had remained at the starting point, would however point out that only twelve days and nights had elapsed since both travellers had set out.