Here are great articles for Aset and Nebet Het from Henadology blog:
Here is Aset’s:
http://henadology.wordpress.com/theology/netjeru/isis/
Here is Nebet Het’s:
http://henadology.wordpress.com/theology/netjeru/nephthys/
One bit that caught my eye was this: (Meeks, Mythes et Légendes du Delta, §7). A fragmentary text concerning a lamp-lighting festival celebrated in Letopolis (Ibid., §18) relates an incident in which Nephthys hides herself from Seth in the water at night, but is discovered by him when he lights a lamp with the oil of the abdu fish, whose characteristic function is to swim before the solar vessel and warn Re of the approach of Apophis; note that this fish is said to have been born on the last of the epagomenal days, which is also the day of the ‘birth’ of Nephthys (Meeks, p. 230).
I would love to find a date for this festival. Set and Nebet Het beating Apep festival with lamps. How awesome is that?
Fiercely Bright One 
I actually got hold of the book again so that I could check this for you, and unfortunately the text gives no date for the festival. It’s organized by places, rather than like a calendar, though it mentions festivals associated with a given town; plus, it’s very fragmentary, of course. Anyhow, thanks for the great blog!
Thank you for checking! Well, maybe adding lamps and this myth to Her Birthday celebration would be a good way to incorporate this into Her worship. Thank you for all of your hard work on Henadology!