as for dates, Samhain occurs on the flip side of Beltane,which is April 31, or May 1 and corresponds to the other cross-quarter days (as they ae called) Imbolc (February 2) and Lammas (August 1) --all fall roughly, more or less, kinda, exactly between the solstices and equinoxes...which themselves vary as to what exact dayss they fall upon...it seems to be easier to assign a day than to hold them on their true times:
"true" samahin for example occurs when the sun enters 15 degrees of Scorpio; this is true for the others as well:
Lammas, 15 degrees Leo
Imbolc, 15 degrees Pisces
Beltane, 15 degrees Taurus
BTW these four signs also correspond to the four animals commonly used in Wicca to represent the four directions: eagle, lion, serpent, and bull...