It is very difficult for me to understand how anyone could say that a definition of creation day length other than a normative day is not an exception to our doctrinal standards. I believe that the WCF authors were defining days in Scriptural terms. Also in Genesis 5, Adam's genealogy sheds similar light on the definition of day in the creation account. Verse 3 states that Adam lived 130 years and then Seth was born. There is no reason to think otherwise than that time in Adam's life was measured from the moment of his creation.
Normative days flow into and make up normative years.
Further, in verse 5, we read Adam's life spanned 930 years. We have no reason to doubt God's honesty. When Scripture states that the entirely of Adam's life was 930 years we can expect that time to include the sixth and seventh days of creation. Added to this evidence is the Fourth Commandment in which God ties in resting on the seventh day with God's resting on the seventh day of creation. There is no reason to believe that the length of creation days is at variance with the length of subsequent days.