A response to that post, along with a screenshot of the statute may have me correct myself.
It may be true that there is no legal penalty associated with failing to register within 90 days. But, could that put you in the category of illegally possessing a regulated firearm?
If so, the penalty is pretty harsh. It's a misdemeanor and if convicted can be up to 5 years in jail and up to a 10k fine, or both.