Well, if I took bad advice, I would be upset at myself, not the website.

Anyway, I took a look at the Canadian website,   (You need to Login or Register; to see if I was mistaken. Turns out it reads that the RABC must be valid on the date of the crossing into Canada. It is a border crossing permit. No mention is made of any need for it to be valid during the entire stay.

While I don't doubt Bill's conversation, border officers don't really deal with RABC crossings. If it were me, I would use it. It's valid and paid for.