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Everywhere the word yom is used in the OT, it simply means an ordinary day.

I'm sorry, woollyone, but you're mistaken. Look at the various meanings of yom used in the Bible. Here is a list of 64 verses where the King James translators interpreted yom to mean a period of time.
It's also worth noting that most translations, strangely enough, mistakenly place the definite article in front of yom. In Hebrew, the definite article is the word ha while the indefinite article is implied when the definite article is absent.
Here is Genesis 1:19 from one of the literal translations that says "And there was evening, and there was morning -- a fourth day." There is a big linguistic difference between saying "a fourth day" and "the fourth day." Even the literal translations add words that are only implied in Hebrew, which is a very sparse language. A hyper-literal translation of Genesis 1:19 would read: "Evening, morning, a fourth day."
Thus, even if you insist upon yom meaning a 24-hour day, it doesn't necessarily mean that the days were sequential.
If you're going to point to the use of "evening" and "morning" to prove an absolute 24-hour day, note that they also have multiple meanings. See this link for evidence from the Bible supporting this fact. Here is a quotation:

If we use the more basic meanings of the words per the figure above, where evening is called 'ereb because when the sun goes down, vision becomes blurry and disordered and with the break of day it clears. Thus we have;
And the mixing and the breaking forth were the ____ time.

Which has caused some to propose.
"And from chaos/disorder to order, the ____ time."

Therefore the reader can possibly chose from any of the above, which ever seems to connect with them the most. Referring back to Fig 1 from Strong's, you will note that "age" is also a valid translation for yowm, but the authors have used "time" or "phase" since these are our preference.

Finally, the creation account is most likely written as poetry. That doesn't mean that it's not literally true, just that the literal truth is written in poetic form and needs to be interpreted as such. What some liberal scholars see as separate and conflicting accounts of creation in Genesis is actually a large block of poetry built on the Hebrew poetic style of repetition and parallism.
Reasonable people can disagree whether the creation account is poetic because, while it contains the basic elements of poetry, it doesn't contain some of the more complicated Hebrew poetic structures that are found elsewhere in the Bible. Based upon my (relatively meager) formal training and continued study of Hebrew, I see the creation account as poetry but I'm not going to stake that as a hill to die upon.
Please be open to the fact that yom has multiple meanings, even in the creation story. Psalms 19 says that "The heavens declare the glory of God, and the sky above proclaims his handiwork." What God shows us through his creation (general revelation) is no less true than what he shows us through his special revelation (God's written word).
Once you get past what I consider to be a man-made literal 24-hour day tradition, you will find that there is no conflict between real science and the Bible, and a whole new universe is literally opened up to you.
May you enjoy all of God's peace, joy, and blessing, my brother in Christ. For in him, we are made as one.