They knew what evening and a morning was...and those two put together = one day. It really isn't rocket science.
1 1 In the beginning God created the heavens and the earth. 2 The earth was unformed and void, darkness was on the face of the deep, and the Spirit of God hovered over the surface of the water. 3 Then God said, “Let there be light”; and there was light. 4 God saw that the light was good, and God divided the light from the darkness. 5 God called the light Day, and the darkness he called Night. So there was evening, and there was morning, one day.
I don't know if these things are correct by 2 pillars, and my view has always been the gap (truth). 😉 But it seems plausible that light could of been more than 12 hours in eternity. Was time even put into action here?
And the reason why I think this is because Day ...
H3117
יום
yôm
BDB Definition:
1) day, time, year
1a) day (as opposed to night)
1b) day (24 hour period)
1b1) as defined by evening and morning in Genesis 1
1b2) as a division of time
1b2a) a working day, a day’s journey
1c) days, lifetime (plural)
1d) time, period (general)
1e) year
1f) temporal references
1f1) today
1f2) yesterday
1f3) tomorrow
Part of Speech: noun masculine
A Related Word by BDB/Strong’s Number: from an unused root meaning to be hot
H3118 is a 24 hour period.
Night is interesting..
H3915
לַיְלָה לֵיל לַיִל
layil lêyl layelâh
lah'-yil, lale, lah'-yel-aw
From the same as H3883; properly a twist (away of the light), that is, night; figuratively adversity: - ([mid-]) night (season).
Total KJV occurrences: 233
Sounds like a happening or interruption? Of some kind during the day that caused adversity to seperate night from day. The rebellion in heaven?
Am not a scholar by any means but I find this thread interesting.