He knew yom as referring to some period of time. yom has a wide range of meanings in Hebrew.
"First, one must understand that the Hebrew language is not nearly as diverse as our English language. Whereas our vocabulary is around half a million, the Hebrew language has only 8,700 words. The French language, one of the poorest modern languages in vocabulary and the language of choice for diplomats, has just about 40,000 words or over 4 times the amount of words that Ancient Hebrew has.
Many of the Hebrew words could be considered duplicates with only slight differences. Thus, words which contain multiple meanings are common. Such is the case with the word Yom.
It is interesting to note that in 67 verses in the Old Testament, the word Yom is translated into the English word "time." For instance, in Genesis 4:3, it says "
And in process of time it came to pass, that Cain brought of the fruit of the ground an offering unto the Lord." In this instance, Yom refers to a growing season, probably several months. Again, in Deuteronomy 10:10, it refers to a "time" equal to forty days. In I Kings 11:42, it says "
And the time that Solomon reigned in Jerusalem over all Israel was forty years." In this case, Yom translated as the word "time" is equivalent to a 40 year period.
In Isaiah 30:8, it says "
Now go, write it before them in a table, and note it in a book, that it may be for the time to come for ever and ever." In this case, Yom is equal to "forever." How long is forever? An infinite number of years...billions upon billions upon billons of years. If Yom can equal trillions of years here, then why not billions of years in Genesis? ........
Other Uses of Yom
Day is not the only translation for the word Yom. Here are some other uses.
Time
It is interesting to note that in 67 verses in the Old Testament, the word Yom is translated into the English word "time." For instance, in Genesis 4:3, it says "
And in process of time it came to pass, that Cain brought of the fruit of the ground an offering unto the Lord." In this instance, Yom refers to a growing season, probably several months. Again, in Deuteronomy 10:10, it refers to a "time" equal to forty days. In I Kings 11:42, it says "
And the time that Solomon reigned in Jerusalem over all Israel was forty years." In this case, Yom translated as the word "time" is equivalent to a 40 year period.
In Isaiah 30:8, it says "
Now go, write it before them in a table, and note it in a book, that it may be for the time to come for ever and ever." In this case, Yom is equal to "forever." How long is forever? An infinite number of years...billions upon billions upon billons of years. If Yom can equal trillions of years here, then why not billions of years in Genesis?
Year
Four times in the Old Testament Yom is translated "year." In I Kings 1:1, "
David was old and stricken in years..." In 2 Chronicles 21:19, "
after the end of two years" and in the very next verse "
Thirty and two years old." Finally, in Amos 4:4, "
...and your tithes after three years." In each case, Yom represents years, not days.
Age
Eight times in the Old Testament Yom is translated "age." These range from sentences like "
stricken in age," meaning old age (Genesis 18:11 and 24:1; Joshua 23:1 and 23:2), and other times it says "
old age" (Genesis 21:2, Genesis 21:7). Genesis 47:28 refers to "
the whole age of Jacob," therefore yom here refers to an entire lifetime. In Zechariah 8:4, it says old men and women will sit in the streets of Jerusalem, "
each with cane in hand because of his age."
Ago
One time Yom is translated "ago." 1 Samuel 9:20 says "
As for the donkeys you lost three days ago, ..."
Always
Four times yom is translated as "always," in Deuteronomy 5:29, 6:24, 14:23, and in 2 Chronicles 18:7. Always here can be interpreted as a lifetime...for instance, we are to keep the commandments of the Lord always (Deut. 5:29).
Season
Three times yom is translated "season." In Genesis 40:4, "
...and they continued a season in ward." Again, in Joshua 24:7, "
dwelt in the wilderness a long season," and in 2 Chronicles 15:3, ".
..a long season Israel hath been...". In each case yom represents a multi-month period.
Chronicles
When used in conjunction with the word dâbâr, yom is translated "chronicles" (27 times).
Continually
When used in conjunction with kôwl, yom is translated as "continually" (11 times). Once, in Psalm 139:16, it is translated continuance (without the kôwl).
Ever
Ever is used to represent a long period of time, such as in Deuteronomy 19:9, "
to walk ever in his ways." Nineteen times Yom is translated "ever." The old testament uses "for ever" instead of the word forever. In sixteen cases of use of the word ever, for is placed before it, indicating a infinite period of time. I will not list them all (consult Strong's Concordance for a full listing) but here is an example. In Psalm 23:6, it says "
Surely goodness and mercy shall follow me all the days of my life; and I will dwell in the house of the Lord for ever." Here Yom is translated as the final word of this verse,
ever. Thus, Yom in this verse, and 16 others, represents eternity.
Evermore
In one instance, when yom is used in conjunction with kôwl, Yom is translated "evermore." Deuteronomy 28:29, "
...and thou shalt be only oppressed and spoiled evermore;" thus representing either a lifetime or eternity.
Word Usage in the Old Testament
As you can see, Yom is used in a wide variety of situations related to the concept of time. Yom is not just for days...it is for time in general. How it is translated depends on the context of its use with other words."
https://www.oldearth.org/word_study_yom.htm