This is also called molad Ba Ha Ra D, because it occurred on Day 2 (yom Beis), 5 (Hei) hours, 204 (Ra D) parts ( pm).
Because this is just before midnight when the Western day begins, but after 6 pm when the Jewish calendrical day begins (equivalent to the next tabular day with the same daylight period), its Julian calendar date is 6/7 October 3761 BCE (Gregorian: 6/7 September 3761 BCE or −3760).
In the section Sanctification of the Moon (11.16), he wrote of his choice of Epoch, from which calculations of all dates should be made, as "the third day of Nisan in this present year ...
which is the year 4938 of the creation of the world" (March 22, AD 1178).
He [the questioner] thought that Rav Nahman wanted to dispose of him anyhow, but when he went and studied it thoroughly he found that it is indeed taught [in a Baraita]: In the Diaspora the Greek Era alone is used. In the 8th and 9th centuries AD, the center of Jewish life moved from Babylonia to Europe, so calculations from the Seleucid era "became meaningless".