Day 11: Festivals, days, and times sacred to this deity“Whichever of the youths is judged to be the most handsome goes round the walls at the feast of Hermes, carrying a lamb on his shoulders. Hermes Promakhos (Champion) is said, on the occasion when an Eretrian fleet put into Tanagra from Euboia, to have led out the youths to the battle; he himself, armed with a scraper like a youth, was chiefly responsible for the rout of the Euboians. In the sanctuary of Promakhos (the Champion) is kept all that is left of the wild strawberry-tree under which they believe that Hermes was nourished.” (Pausanias, Description of Greece)
11. Traditionally, days to offer to Hermes regularly took part on the 4th day of each month, with 4 being a sacred number to Him as well. Wednesdays are also auspicious as a liminal middle day in the week (it is also sacred to Odin and Cernunnos too, named after Woden). Like Hekate and other psychopompic deities, Hermes favours liminal times, such as dawn or dusk, midday and midnight. These in-between times are opportunities to bend reality, manifest magick, to reach between the veils and travel the realms. Hermes is also given honor at the dark moon, or deipna...alongside Hekate at crossroads in their twin chthonic aspects.
There was a Greek festival specifically dedicated to Hermes, the annual Hermaia; an initiatory time with rituals taking place in gymnasiums. Contests of physicality and skill took place, alongside gambling which usually follows along with sporting events. There is some evidence that also suggests Hermes was part of the festival at Eleusis, escorting the Goddess Persephone out of Hades and reuniting with Her mother, Demeter in the annual festival of Thesmophia.
The Romans in their adoption of Hermes as Mercury celebrated the Mercuralia, or the Ides of May (May 15th) believed to be His birthday. Suppliants would take water from a fountain in Porta Capena at aqua Mercurii, to asperge boats with bay laurels in blessings of commerce and profit. Some modern practitioners celebrate His birthday as April 4th, which makes me wonder if there is a connection between this and April Fool's on the 1st, a modern, secular holiday. I believe today, July 11th (7/11) is a sacred day for receiving blessings of Hermes in luck.