S1 Yom 8 - Sabbath

Sabbath and the 8th day of the Biblical month starts at:
sunset on the 20th through sunset on the 21st of the Gregorian month(s).

Exodus 31:13

Say to the children of Israel that they are to keep my Sabbaths; for the Sabbath day is a sign between me and you through all your generations; so that you may see that I am the Lord who makes you holy.

(The 1st Day of the Seventh Month on the Biblical Hebrew Calendar is Yom Teruah and is commanded to be a rest day.  Leviticus 23:24, Numbers 29:1)

Six workdays must be counted off to establish the 1st Sabbath of every month, so unlike any other month, the 1st Sabbath falls on the 8th of the Hebrew Calendar in the 7th Month instead of the usual 7th of any other Hebrew month.

Exodus 23:12

For six days do your work, and on the seventh day keep the Sabbath; so that your ox and your donkey may have rest, together with the son of your servant and the man from a strange land living among you.