Scholarship seems to reinforce my findings that Oympiad 109, Year 3, Gamelion 20 = January 24-25th 341 BCE.
“He was born on the twentieth of the month of Gamelion (24 January 341)74 […] 74The debate over the exact date of his birth was definitively resolved by Alpers 1968.” (Algra, The Cambridge History of Hellenistic Philosophy 43)
“Date of the birth of Epicurus, according to Apollodorus […] that is, under the seventh archon from the archon of the year of the death of Plato, Theophilus. The tenth of Gamelion however, January 14, and the twentieth, January 24, are also assigned as the dates of birth.” (Origines Kalendariæ Hellenicæ; or, the history of the primitive calendar among the Greeks, before and after the legislation of Solon, Volume 2, 97; 1862)