So 3 Cups in a row is a dynasty not 4 ?
Eh, it's one of those words (like so many in sports) that's gotten watered down with overuse. It's like, we had so many "stars" of the sports world that we need "superstars", and even those have long been a dime a dozen. Or that the list of people at some point designated an "all-time great" is pretty endless.
To me, the term "dynasty" has always been influenced by its actual (non-sports) meaning: a line of hereditary rules. Something where power and prestige are passed from generation to generation. To me, the UCLA Bruins with 10 national championships in the 60's and 70's are the very definition of a dynasty. Sure they had the same coach over that entire run, but they had complete roster turnover a few times in the course of it.
To me, a hockey team that wins four Cups in 10 years, with the torch being passed from one captain to another, looks more like a dynasty than one that wins four straight Cups all with the same core.
I get that my view is idiosynratic here, but since we're just using the term however we want it seems silly to argue over three vs four.
All that said, I would definitely argue that if we do set a bar at four, it doesn't need to happen all in four or five or even six years. I'd be good with it happening within a decade, and definitely within 8 years, as long as there aren't any huge gaps. Such a team looks like a clear "dynasty" to me.