When do you consider revisiting messaging hierarchy for products?

A few thoughts. It's best to be in front of this challenge then behind it. If you are the PMM for a product, and you are waiting till the product as outgrown the messaging to then change the messaging... not great. Your messaging should ideally be out in front of the product. It should be telling the story of the product today and then near future. Selling the vision, making sure you're unique, and making sure buyers and customers have confidence in the future of your product. The tail should wag the dog within reason.

This isn't always possible though I know. So I'd say at least quarterly you need to make sure product messaging is updated. I have a monthly or quarterly sync with our web team to make sure the that what our product pages say is up to date with the status of our current products and messaging.