You admit, then, that yom has more than one meaning; it is only your interpretation which insists that -- in this particular usage -- it must be understood to refer to a period of 24 hours.
Wrong, it is the usual understanding. If you take all of the instances in the Hebrew Scriptures of the word YOM and compare them WITH THEIR QUALIFIERS then the only definition that you can REASONABLE come up with is a literal 24 hour day. To say otherwise is to step outside of the bounds or reason and try to force a meaning on a text that the text does not, will never, and was never meant to have. And why would one do that unless they were trying to let fallible "science" interpret the Bible rather than let the Word of God interpret science?
It is your choice, by the way, which you choose to accept. But for pitys sake, dont' try to say that the Genesis account literally means anything other than a 24 hour period of time. That would be eisegesis, not exegesis and would be very very poor biblical scholarship.
Gen 2:2 And on the seventh day God ended his work which he had made; and he rested on the seventh day from all his work which he had made.
Gen 2:3 And God blessed the seventh day, and sanctified it: because that in it he had rested from all his work which God created and made.
So how long a period of time is this seventh day, the Sabbath?
Heb 11:3 Through faith we understand that the worlds were framed by the word of God, so that things which are seen were not made of things which do appear.