Yekke2, your question about starting the night before at nightfall has been addressed. Not by any Shu”t I’m familiar with, but by an old badchan routine. Perhaps you haven’t attended many chassidish weddings’ mitzvah tantz this time of year?
Q. Farvooss on nittel, a goyishe choggeh (as in chag) do we begin the night before, and Peerrim, a Yom Tov bei Yidden, we celebrate the night after (the seuda usually goes on through the night of 15 Adar) ??
A. Veill nittel halt men nuch a Yid- (we celebrate after a Jew), and Purim we celebrate after a goy- (we’re celebrating the hanging of Haman) !!