Day 11 - Festivals, Days, and Times Sacred to Hekate
Hecatesia (celebrated on different dates - August 13 or 16 - likely related to the Nemoralia and not historical , November 16 - another likely modern celebration)
Dark/New Moon - last day of the lunar month
Hekate's Night - November 16th - likely a modern celebration
Day of Hekate at the Crossroads (October 31 or November 30)
Deipnon - The last day of the calendar month
December 31 - Roman, however, once again, no historical proof can be found.
I have collected the above dates over the years, but have not found that these, with the exception of the last day of the lunar month, Hekate's Deipnon, have any historical basis. That being said, we can celebrate our goddesses whenever we choose, for the most part.
For myself, I celebrate the monthly Deipnon on the Dark of the Moon, which you will find marked as the New Moon on your calendar. Again, for myself, the New Moon is when I can see the first crescent in the sky. I leave food at a crossroad after my ritual.
I have also celebrated Hekate on the 13th of August, but now celebrate the Nemoralia which honors the goddess Diana. I do include Hekate in my celebrations because it is also known as the Festival of Torches, dogs were honored, sacrifices were made of small sculptures of mothers and children, and women as well as slaves were freed from their duties for this festival. It makes sense that this evolved into a celebration of Hekate in our modern times.
Hekate's Night on November 16th is another time I celebrate Hekate, in addition to honoring Her on Hallows, October 31st. Over many years these dates have become an important part of my devotional practices for Her.
Celebrate as you feel drawn to.