Since this million/billion years discussion falls into the category of the "improper sense that days refers to a certain space of time rather than a natural day".  Then, the fact that birds were created on the same day as the sea creatures, and a day before the land creatures creates a problem for the long time interval.   Because, I contend that there is no way that the allotted time between days is allowed to fluctuate.  

That means that if you believe the earth is 5 billion years old, then each day would equal 5 billion divided by 7.  That means that birds were flying around and mammals were swimming in the sea for 7142857.1 years before God created land creatures.  It also means that God rested on the seventh day for 7142857.1 years, which was 7142857.1 years after he created adam and eve.  

I cannot believe that only days 1-4 allow for billions, and days 5-7 can be different/less to cooperate with so called findings of modern science and lets face it, reason.  So, I cannot believe that millions/billions is possible or reasonable.

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