There are other, even older, associations with May 1st in Celtic mythology. Years later, the Tuatha De Danann were conquered by the Milesians on May Day. May Eve was also the occasion of a fearful scream that was heard each year throughout Wales, one of the three curses of the Coranians lifted by the skill of Lludd and Llevelys. By the way, due to various calendrical changes down through the centuries, the traditional date of Beltane is not the same as its astrological date. This date, like all astronomically determined dates, may vary by a day or two depending on the year.
Some Covens prefer to celebrate on the old date and, at the very least, it gives one options.
This may also be a consideration for Covens that need to organize activities around the week-end. This date has long been considered a 'power point' of the Zodiac, and is symbolized by the Bull, one of the 'tetramorph' figures featured on the Tarot cards, the World and the Wheel of Fortune. Christians have adopted the same iconography to represent the four gospel-writers. But for most, it is May 1st that is the great holiday of flowers, Maypoles, and greenwood frivolity. And those who ancient lines did ley Will heed this song that calls them back.