Question: Genesis 1:5 says that God ended the first creative day with the expression, "the evening and morning were the first day". Each successive day ends with the same expression. Does this indicate that the creative days were 24 hours in length?

Answer: 
There are two indications that the "days" of Gen 1 are literal 24-hour days:

* The regular repetition of formula, "and there was evening and morning, the nth day".
* The use of the specific numeral associated with the word "day", first day, second day, third day, etc.

The latter point needs further comment.

The Hebrew word "day" is יוֹם (yom). It is used in at least two distinct senses in the OT. (The BDB entry is too large to reproduce here so I will summarize).

* an indefinite period of time or a time past, eg, Gen 3;14, 17, 4:3, 14, 5:1, 11, 6:4, 9:29, 18:11, etc.
* When accompanied by a numeral, the word ALWAYS means a literal 24 hour period of time, eg, Gen 2:3, 7:4, 11, 12, 17, 8:3, 4, 12, 14, 17:12, etc.

In summarizing this situation,. it was Professor Barr (at Oxford) who wrote to to Mr David C C Watson in Illinois, dated 23 April 1984, who said -

> 
> “… probably, so far as I know, there is no professor of Hebrew or Old
> Testament at any world-class university who does not believe that the
> writer(s) of Genesis 1–11 intended to convey to their readers the
> ideas that creation took place in a series of six days which were the
> same as the days of 24 hours we now experience, the figures contained
> in the Genesis genealogies provided by simple addition a chronology
> from the beginning of the world up to later stages in the biblical
> story, Noah’s flood was understood to be world-wide and extinguish all
> human and animal life except for those in the ark.”
> 
> 
> 

I agree. The writer of Genesis writes about literal 24 hour periods of time.
The expression 'day' is defined within the context of the passage. The definition is 'the evening and the morning were the first day' and so on.

Thus 'day' means 'evening and morning'.

And therefore 'day' contains 'night' within it. The daytime brackets the night period.

That is to say, light contains the darkness. Light brackets the darkness. Light surrounds the darkness.

And the darkness, though it be present, does not prevent the morning breaking into a new day.

There is the closure of one phase, then a period of darkness. Then another period, a new phase, begins. This, all of this, is 'day'.

And the first three days cannot be measured in terms of time. There was no sun. There was no moon. *And there was no observer on earth to observe the event.*

It is impossible, under such circumstances, to state any calculated data whatsoever about the events. To do so, is just speculation.