PERMANENT RESIDENCE - mandatory to be married 5+ years?

I am a South African citizen, married to an American and we live in the US. We've been married 4 1/2 years and I was wondering if he can apply for permanent residence based on section 26(b) for spouses. Nowhere in the instructions or on the application does it state that we have to be married for 5+ years, but I've read it on some of the blogs.
Can someone clarify this for me? Thanks!!

I'm pretty sure 5+ years is mandatory. When I applied we weren't married for 5 years and I've got my permit only because we are having kids together and therefore I do have SA relatives. The entire application process took 4 years!
Not sure this helps but if you don't have kids together you rather assume 5+ is mandatory.

Cheers
Andreas

You know this one trumps me too! I believe it's from regulation 3 (1) of the Act (separate document. It's the one that was amended last year June). Problem is originally (old regulations) said 5 years here, amended regulations say 2 years. But vfs and dha seem to be intent on disregarding this.

Anyway, hope that helps you!