The most likely date for her festival will be around the first fortnight of the month of August, the first half of that month, most people tend to say, that this occurs at the 13th of August.
Hecate is the goddess of the night, of mystery, magic and the goddess of the doors between this world and the other, she is considered to be the patroness of those who practiced witchcraft,however in those times, there was no such thing as witches, or i might say, people playing around pretending to make spells. This is a goddess connected to the mediterranian peoples who practiced magic in natural ways, for people who were devoted to only a limited aspect of shamanism.
People used to make offerings to Hecate, in places were two paths would cross, an embodiment ofthe two routes, the two worlds, or to the two realities, with many torches, the festivities would begin.
Despite being a goddess of the night, the festivities in her honor, would begin at every morning in the days of the new moon. Many people think that goddesses like this one, are associated to the nights of full moon, but because these kind of goddesses are also the goddesses of mystery and such stuff, they are associated to the dark nights of the new moon.
Whispers of Yggdrasil 