Please read the whole article. If it only takes a "few hours" to create incriminating "evidence" (read, something that didn't exist) - it must be clearly proclaimed as such to the world.
I believe you are referring to this quote (correct me if not):
"In fact, in the early DKIM configurations were kind of a joke: mail providers chose DKIM signing keys that were trivial for motivated attackers to crack. Back in 2012 a security researcher named Zachary Harris pointed out that Google and several other companies were using using 512-bit RSA to sign DKIM. He showed that these keys could be “cracked” in a matter of hours on rented cloud hardware, and then used these keys to forge emails from Larry and Sergey.
Providers like Google reacted to the whole “Larry and Sergey” embarassment in the way you’d expect. Without giving the implications any serious thought, they quickly ramped up their keys to 1024-bit or 2048-bit RSA. This stopped the forgeries, but inadvertently turned a harmless anti-spam protocol into a life-long cryptographic authenticity stamp — one that can be used to verify the provenance of any email dump, regardless of how it reaches the verifier."
Note that the "few hours" attack here is only relevant if they were using easily crackable 512-bit keys. The author of this article suggests (and I agree) that the 1024 or 2048 bit RSA keys are not easily crackable. (see https://crypto.stackexchange.com/a/42830)
Maybe you are suggesting that someone could sign emails using the old crackable 512-bit keys. And they could, although we should disregard this as "not verification" given the weak keys. The article links to https://github.com/robertdavidgraham/hunter-dkim#short-dkim-... - which verifies an email using a since-rotated 2015 key (which was 2048 bits), although that github erroneously states that Google was using 1024 bit before that (they were using 512).
I would concede that the notion of "sometimes we should disregard some DKIM verifications based on the key length" is not easy to grasp and that email verification stories in the media could become muddier and harder to present. I would hope that interviewing experts gets you a reasonable estimation of how likely an email is to be legitimate.
