Here is just a quick observation on Yom:
It is used in three distinct ways in Genesis 1.
1. 24 hour day. Genesis 1:14 (NAS): Then God said, “Let there be lights in the expanse of the heavens to separate the day from the night, and let them be for signs and for seasons and for days and years;”
Example: Sunday is the first day of the week.
2. Daylight portion of the day. Genesis 1:16 (NAS): God made the two great lights, the greater light to govern the day, and the lesser light to govern the night; He made the stars also.
Example: How did your day go?/ Work while it is day.
3. Unspecified period of time. Genesis 2:4 (NAS): This is the account of the heavens and the earth when they were created, in the day that the Lord God made earth and heaven.
Example: “Back in my day…”