Richard,
Although the transliterated in Genesis 1:5 is the same for both occurrences, yet the Hebrew words differ slightly. (source: - Biblehub.com)
First occurrence י֔וֹם yō·wm
Second occurrence י֥וֹם yō·wm
Hi Jay. I see what you are referring unto. Those are cantillation marks (te'amim). Their purpose is with regard to the chanting of the Hebrew Scriptures. In simplest terms, they are musical notation. They serve to denote intonation and pause in the chanting of the Scriptures. They have no function whatsoever with regard to the meaning of the word.
So, by my reasoning, the meaning of both words in the Hebrew text have very different meanings.
I do understand your reasoning, however they are in fact the same word. I guess I can't fault you for paying attention to every "jot" and "tittle".
Have you ever examined the Isaiah Scroll found amoung the DSS? You will notice the lack of both the nikud and the te'amim in it. Link:
http://dss.collections.imj.org.il/isaiah
Genesis 1:5 first occurrence י֔וֹם yō·wm
Genesis 1:16 first occurrence הַיּ֔וֹם hay·yō·wm
Genesis 1:18 first occurrence בַּיּ֣וֹם bay·yō·wm
The subtleties between Genesis 1:16 and 1:18 I am ignorant on, but the context of both verses suggests to me that both occurrences are speaking of a period of time associated with the sun while it is casting light over the visible earth as seen from its perspective.
1:5 yom, is YVM : Yod - Vav - Mem.
The nikud (vowel point) is the dot over the vav, it is a kholem malay (aka vav holem). Thus giving us a transliteration of yom.
The te'amim are the two dots over the yod, or first letter. It is a zaqef qaton, again in the simplest terms, it is a musical notation.
1:16 ha-yom : hayom : HYVM : Hey - Yod - Vav - Mem The first letter, Hey, is the prefixed definite article. And of course, yom as above follows. Under the Hey, there is a horizontal line, that is the nikud Patakh ; a : as in father. Hey Patakh form ha- : The dot in the Yod, is a dagesh. In this case, a dagesh hazak, which is the result of the presence of the definite article to keep this simple. The rest is as described above regarding 1:5.
In transliteration, I generally would transliterate the 1st occurence in v16 as ha-yom, denoting the prefix ha-. By separating it in such manner, it renders such more readily visible. When translating as I did in my previous reply, I generally render it as: the-day, further making all the more apparent the relationship.
1:18 ba-yom : bayom : BYVM : Beit - Yod - Vav - Mem In this occurrence we have the preposition Beit in prefix to yom. ba-yom : in-the day. When the preposition beit introduces a definite noun, it forms a contraction with the definite article.
Example: Genesis ; be-re'shit ; in-the beginning.
The letter Beit is one of several that have two sounds, hard and soft. Beit without a dagesh, is veit, in that it is soft frictive as in v. With a dagesh (dagesh qal), it carries the hard b sound.
So we have Beit Patakh, ba- : The horizontal line beneath Beit is the nikud Patakh, "a" as in father again as we saw above. The rest of yom, is as described above with the exception of another cantillation mark. The backwards looking L below the Yod is a shofar holekh, again, in the simplest terms, musical notation which has no effect upon the meaning of the word.
And yes, you are correct that all three of these occurrences are referring to a day as in the daylight hours. Yom refers to both the daylight hours and a 24 hour period (and more, but I want to keep this on the simpler side). It is context, or a qualifying / associated word that determines the difference as to what period of time that yom is referring unto.
Hopefully I have offered a little help and perhaps a little insight.
For me the difference between Genesis 1:5 and Genesis 1:16, 18 has to do with the respective reference time frames being spoken about. Genesis 1:5 is with respect to the reference time frame in God’s domain, while both Genesis 1;16, 18 are with respect to the reference time frame within man’s domain.
I can see how you could take it there. However I respectfully disagree.
Sadly, I have not found the tools/references which allows me to compare Hebrew words and their respective Hebrew Root.
For myself, it required learning a little Hebrew to know and understand.
What I would suggest to you: If you don't have a hardcopy interlinear, get one. From there, begin to learn the Hebrew Alef-Bet. And the nikud. Any decent hardcopy interlinear will have the Alef-Bet and a chart of the basic nikud.
From there, have discussions with people such as myself slowly increasing your usage of transliterated Hebrew. That alone will help you immensely. And, it provided a system of checks and balances in doing so with people who have at least a minimal working knowledge of the language.
It seems that the Hebrew text does not show the same on this forum site, as on the Biblehub.com site and the differences may not be as easily observable.
It shows up fine on my computer. However I also a couple few Hebrew fonts installed. If it doesn't show up properly, that is due to a lack of the proper font.