Here is something that I believe is relevent to this conversation.

Normally "yom" is used in Scripture to mean a 24 hour day. But there are exceptions such as Is. 61:2 where it is used for longer periods of time. Or in the case of Genesis 2:4, where it is used as an idiom "when".
However, in Genesis chapter one it must be interpreted as a 24 hour period.
1.) Elsewhere, whenever "yom" is used with a number, it means 24 hour periods.
2.) The Decalogue bases the teaching of the Sabbath day on the six days of creation and the seventh day of rest.
3.) From the 4th day on, there are days, years, signs and seasons, suggesting that the normal system (24 hour day) is entirely operative.
4.) If "yom" refers to an age, then the text would have to allow for a period of "night". But few would argue for the night as an age. It seems inescapable that Genesis presents the creation in six days.

(From Creation & Blessing 'A Guide to the Study and Exposition of Genesis by Allen P. Ross Page 109)