'And there was evening and there was morning – the [number] day' is the concluding phrase for each of the Genesis six days of creation (Genesis 1:5, 1:8, 1:13, 1:19, 1:23, 1:31).
When that phrase is interpreted in its most strict and literal sense, it often doesn't make sense when applied in context. For example:
Then God said, 'Let the land produce vegetation: seed-bearing plants and trees on the land that bear fruit with seed in it, according to their various kinds. And it was so. The land produced vegetation: plants bearing seed according to their kinds and trees bearing fruit with seed in it according to their kinds. And God saw that it was good. And there was evening, and there was morning – the third day'. (Genesis 1:11-13).
God said 'Let the land produce,' so a strict literal reading of evening-and-morning into that passage would lead us to believe that the seeds from all the different kinds of plants and trees produced abundant vegetation between evening and morning of one particular day. Obviously, this is not a sensible interpretation because we know that seeds do not germinate, grow and produce abundant vegetation overnight.
In the modern world, a full 24-hour day is understood to be from sunrise to sunrise, but in ancient Israel, it was from sunset to sunset. We say morning to evening. They said evening to morning.
The repeated phrase 'And there was evening' was a Hebrew way of saying that something new was started. When used together with the phrase 'and there was morning' it was a Hebrew way of saying that something was started and it was finished. The full phrase marked time span from the beginning of something to the end of something, which may or may not have been 24-hours, depending on the context.
It's like when we say, 'With young people leaving in vast numbers, it's a new day for the church ...' or 'At end of the day, the investigation will show who was right ...' or 'That day is gone ...' We know from the context that these statements obviously mean a time longer than 24 hours.
Furthermore, the repeated phrase was used for Days 1, 2, and 3, even though 24-hour time as we know it did not even exist until Day 4, the time when celestial orbits stabilized and earth's dense cloud cover dissipated so the sun was visible.
The Bible says that light was created in Day 1, so there was already light before Day 4, but it was shrouded in cloud cover. From earth's perspective, the sources of light (sun, moon and stars) became visible in Day 4.
The Bible gives the reason why God made the sources of light become visible from earth:
'And God said, Let there be lights in the expanse of the sky to separate the day from the night, and let them serve as signs to make seasons and days and years ... And there was evening, and there was morning – the fourth day' (Genesis 1:14).
This started distinct growing seasons, bird migrations, and human time measurement and navigation.
Time, as we measure it, started in Day 4, so our calendar days didn't even exist in Days 1, 2 and 3. Therefore, the phrase 'and there was morning and there was evening' – used in all six days of creation – does not refer to our calendar days.
'By the seventh day God had finished the work he had been doing; so on the seventh day he rested from all his work. Then God blessed the seventh day and made it holy, because on it he rested from all the work of creating that he had done' (Genesis 2:2-3).
In 'days' one through six, the biblical account of God's creative acts in each period concluded with this phrase: 'And there was evening and there was morning – the [number] day.' But that phrase is missing for 'day' seven.
Because 'day' seven has not yet ended. God is still resting [pausing new creations]. We can confirm this just by looking around at our world. The Bible says that God will resume His creative acts by making a new heaven and a new earth, but for now, changes are only by procreation, evolution (within categories), and physical alterations caused by weather, gravity, and movement of tectonic plates.
Therefore, if 'day' seven is longer than 24 hours, there's no need to constrain any of the other 'days' to 24 hours.
'The Lord God took the man and put him in the Garden of Eden to work it and take care of it. And the LordGod commanded the man, you are free to eat from any tree in the garden; but you must not eat from the tree of the knowledge of good and evil, for when [bə·yō·wm, in the day when] you eat from it you will certainly die' (Genesis 2:16-17).
NOTE: The NIV Bible tries to avoid the problem by saying simply 'when,' but the correct translation is 'in the day when,' as stated in the Hebrew manuscripts and properly stated in most English translations.
Adam did not die in the 'day' he ate the forbidden fruit, so obviously 'day' means more than 24 hours.
Some Christians dodge the clear meaning by saying that Adam died spiritually on that day. Even so, that just means the start of a long time of separation from God. With that kind of reasoning, we could then say that a 'day' just means the start of a long time of species multiplication.
By any honest interpretation, it's clear that a 'day' (yō·wm) means more than 24 hours.
'But do not forget this one thing, dear friends: With the Lord a day is like a thousand years, and a thousand years are like a day' (2 Peter 3:8).
The Bible teaches that God's timing is not on the same scale as our timing. It is much larger! We should not try to squeeze God's majestic unfolding creation over the ages into our puny time frame.