One, YOM, means a literal day, such as when the sun goes up and then the sun sets. But BEYOM refers to a period of the time...
I was debating whether to discuss that angle, decided not, but glad you did. The point that the authors had individual traditions and emphasis, along with your pointing out that the words YOM and BEYOM are not equal, should end this conversation.
When a Christian writer utilized a story, like the Adam and Eve or Noah stories, he almost certainly did so in the same spirit as the original author, a theological/moral tale.
While not an exact parallel, the Grimms Fairy tales preserved an ancient German moral code of sorts. Characters dramatizing values and traditions. Do some children mistake the stories as real? Sure, but as adults we can appreciate them for what they are.
As an aside, it's my view that the Gospel stories are a continuation of the Jewish/Greek affinity for moral tales and can be appreciated as such.