Q. Should one wait to eat supper on the eve of Erev Yom Kippur until night, so he can comply with the mitzva of eating on that day?
A. Shulchan Aruch and Mishna Berura (O.H. 604:1) write that it is a Biblical mitzva to eat on Erev Yom Kippur. However, Poskim disagree whether it starts at night (Sheloh as quoted by Magen Avrohom ibid., Eishel Avrohom), or it begins only in the morning (Biur Hagra and Yad Efraim, ibid.).
Horav Shlomo Miller's Shlit'a opinion is that it is not necessary to wait until night,
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit'a
Important Numbers
