And the evening and the morning were the first day.
And the evening and the morning were the second day.
And the evening and the morning were the third day.
And the evening and the morning were the fourth day.
And the evening and the morning were the fifth day.
And the evening and the morning were the sixth day.
"evening and morning" is like saying "night and day"
'evening' marks the beginning of the night ( dark ); 'morning' marks the beginning of the day ( light )
"evening and morning" is, in effect, saying "one rotation of the earth"
I have never heard anyone dispute that - from day
seven onward - every day since creation ( with a couple of biblical exceptions ) has been a ~24 hour day.
If any of the first week days were longer - at the very least - they would have had to fit into a realistic pattern of acceleration of the Earth as it "spun up" to reach the every-day ~24 hour cycle we are all familiar with.