Sundown - Sundown Day

Genesis 1:5,8,13,19,23,31

5 God called the light Day, and the darkness He called Night. So the evening and the morning were the first day.
8 And God called the firmament Heaven. So the evening and the morning were the second day.
13 So the evening and the morning were the third day.
19 So the evening and the morning were the fourth day.
23 So the evening and the morning were the fifth day.
31 Then God saw everything that He had made, and indeed it was very good. So the evening and the morning were the sixth day.

Nehemiah 13:19

So it was, at the gates of Jerusalem, as it began to be dark before the Sabbath, that I commanded the gates to be shut, and charged that they must not be opened till after the Sabbath. Then I posted some of my servants at the gates, so that no burdens would be brought in on the Sabbath day.

Psalm 55:17

Evening and morning and at noon
I will pray, and cry aloud,
And He shall hear my voice.

A Jewish day began at sundown. Does a day still begin at sundown? There are arguments for sundown, midnight and sunrise. I've looked at them all, and have not come to a firm conclusion.

But the time when a day starts/ends is not mandated in the Bible, so we shouldn't be dogmatic in this area. Be consistent in the one you hold to. Don't flip-flop whenever you want to labor on the Sabbath.