"...grammatically, linguistically, there is no other way that the creation account can be understood."
That seems to be a recklessly strong statement. If you were to say that it is 'clearly the best' interpretation given only the evidence from Scripture I'd probably agree completely. To say that it rules out any other understanding is pretty strong and completely leaves out natural revelation. What is your view of natural revelation by the way? Would you agree that it's a less-reliable yet valid form of revelation and that the 2 revelations, if properly understood, will never contradict each other? And if they appear to then one or the other is being misinterpreted?

I read the link you provided, thanks for that. I seems to me that the author really has 2 arguments:
1. The Westminster Confession says it's 24 hour days
2. The best Biblical exegesis would be 24 hour days

I've already commented on #2. However, #1 seems fallacious. Who cares what the authors of the confession believed Scripture to say? Have we decided that the Westminster Confession is inerrant?

If we are going to argue from authority (not that I really think you were, but please don't think I am either), then isn't this document more authoritative than the document you provided? http://www.pcanet.org/history/creation/report.html
Why weren't these people able to say that 24-hour days were a mandatory interpretation for Presbyterians?

Honest, friendly questions here. I hope that the above doesn't read as argumentative.

Thanks for entertaining these questions.