The 9th of Bysios holds some uncertainty regarding its significance, although it is potentially associated with Dionysos. During this period, Athens observes a Dionysian festival called Anthesteria, marking the first opening of the new wine, following winter. A similar festival is recorded in Plutarch's account of his hometown in Boeotia, not far from Delphi.
It is possible that this festival marks Dionysos’ departure from Delphi, however there are other references associated with Delphi, that refer to the return of Dionysos in the spring after a twelve month absence. It remains unclear whether these two carratives were linked, or viewed seperately. The winter ruler of Delphi could also return in spring if his dominion over Delphi originated from the underworld.
The 9th of Bysios.
Βυσίου [μην]ὸς τὰν hεβδέμαν καὶ [τ]ὰν hενάταν Bysios month the seventh and the ninth
– A Collection of Greek Ritual Norms (CGRN) – Two excerpts from the dossier of regulations of the Labyadai at Delphi $^{5}$
The 9th of Bysios is a day surrounded by uncertainty. It may have some connection to Dionysos, as indicated by festivals like Anthesteria in Athens and similar celebrations in Boeotia mentioned by Plutarch. Accounts suggest that Dionysos returns in the spring after a year-long absence, raising questions about how the winter king of Delphi could also return in the spring. One possibility is that his rule over Delphi was associated with the underworld, symbolizing his return to life. It is also likely that these two mythic strains were never linked to each other, and are intended to be considered seperately.
The exact nature of the 9th of the month remains unclear, but it might have served as a time for specific religious and administrative gatherings. Poetic references further emphasize the association of Dionysos with springtime and the joyous celebrations that accompany his arrival. The 9th as a festival day is common for Dionysos.
The 9th of the month remains more murky, though it may have had some connection with Dionysus (cf. again Rougemont). Both days, not explicitly specified as festivals, may have constituted specific religious and administrative meetings of the group.
929 Rainer papyrus (1st c. b.c. or 1st c. a.d.) (b) Shout aloud to him! We shall sing of Dionysus on these holy days: he has been absent for twelve months, but now the springtime is here, and all the flowers . . .
984A = S318 Himerius, Orations
. . . or as
Bacchiotes
—for so the lyre calls him, meaning Dionysus— when spring has newly shone forth is garlanded with spring flowers and ivy clusters by poets in the Muses’ grip and brought now to the topmost peaks of Caucasus and the vales of Lydia, now to the crags of Parnassus and the Delphic rock, leaping himself and to his Bacchants granting the cry Euius.
Plutarch
Herodotus