Saying that yom is 24 hours is anachronism. At the Chumash times, Jews probably used Talmudic uneven hours: dividing day in 12 parts. Not sure what Egyptians used. Night didn’t have a sundial for such precision so it has 3-4 shifts. Possibly 12 hours correspond to 12 months or general Babylonian method of dividing 6, 60, etc
Interestingly French revolution converted space and weight to metric but they couldn’t concur Jewish time: ten day week and ten hour day wasn’t accepted, but they tried