"Some will argue that the word for ‘day’ in Hebrew, yôm (יום), is not so clear in Genesis 1, because it can have several different meanings. Similarly, in English, the expression ‘in my father’s day’ does not mean a literal day. Dr Steinmann responds that in both English and Hebrew, “context and the author’s or speaker’s intention determine meaning.” Indeed, the phrase ‘in my father’s day’, contains contextual clues as to the meaning of the word day. “One clue is the use of the preposition in which
implies a time during which something happened (i.e. an era) in contrast to another preposition such as on which implies a point in time, a particular day (i.e. on the first day of the week). Another clue is the use of a person who lived in a past time (father’s), again implying a past era. These clues are often obvious to native speakers of a language, but not so obvious to those for whom the language is not native. So, for Genesis, we must be very careful to look for the contextual clues, since no one today is a native speaker of ancient Hebrew.”
When it comes to the six creation days followed by the day of rest, all the creation days close with the phrase, “There was an evening, and there was a morning.” Could this allow for creation days millions of years long, as ‘Day-Age’ theorists teach? Dr. Steinmann adamantly replies, “Absolutely not!” and continues, “Clearly this phrase used in this context notes the day-night cycle, a cycle begun on the first day with the creation of light. Moreover, this phrase is repeated five more times to emphasize that there is a succession of six solar days during which God created the world.”
In technical papers, Dr. Steinmann argued that this phrase is a merism meaning the whole 24-hour day. A merism is a figure of speech where two opposites are used to refer to a whole, e.g. ‘open day and night’ meaning open for the whole time, including dawn and dusk; ‘searched high and low’ means ‘searched everywhere’.
Furthermore, the days have a number. The beginning day of Creation Week is “Day One” (Hebrew yom echad (יום אחד)). This is further support for a 24-hour day. Dr Steinmann explains:
“‘There was an evening, and there was a morning, one day’ essentially says ‘evening + morning = one day.’ In this context day is clearly defined as being a regular (normal-length) day.” CMI
And God saw every thing that he had made,
and, behold, it was very good.
And the evening and the morning were the sixth day.
Genesis 1:31