Q. What date should someone write on the sell of Chometz when it was done after the Shekia (sunset)?
Should one use the non Jewish date?
A. In principle the commonly used document for the sale of Chometz is just a letter nominating the Rabbi to be an agent to sell one’s Chometz as described in it. Even without a date, it would be valid.
However, Horav Shlomo Miller’s Shlit’a opinion is that when the date written was before the actual date of the signing, or Sh’tar Mukdam, it is better.
Rabbi A. Bartfeld as revised by Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu Shlit’a