RE: Were the seven days of creation in Genesis seven twenty four hour periods? - Where do these notions originate?
Yes, the Hebrew "yom" can mean an indefinite period of work, but it can also mean a literal day.
To figure out which the authors meant, we should examine the context. In the context of Genesis 1:4-5 where God creates separates day (yom) from night, and the evening and then morning of the first day follows, it's quite clear the authors were referring to literal days which are light out and have evenings/mornings rather than indefinite work periods which don't:
"And God said, “Let there be light,” and there was light. God saw that the light was good, and he separated the light from the darkness. God called the light “day,” and the darkness he called “night.” And there was evening, and there was morning—the first day."
Christians who accept some of what science has to say balk at this and say it must be mistaken, because otherwise the Bible would be wrong, and they presuppose that it can't be. There is a much simpler alternative explanation: Christianity is false, and the authors of scripture made many such errors in their proclamations about the world because they did not actually have any specially revealed information about it.
I think perhaps you arrive at your "simpler alternative" a little to quickly, wait for the next one for a further discussion of "yom" etc.