Whenever you actually put in the time and effort to learn and understand the abstractions. There are plenty of people who have done so and who are enjoying the benefits of having done so. I'm still a novice by comparison, and I still find my understanding of category theory as implemented in Haskell to make my life easier on a very regular basis, to the extent that coding in other languages for my day job is becoming more and more painful as time goes on.

Well, given that Haskell 1.0 didn't use category theoretic structures in any serious capacity and it's IO was based on lazy streams, I'd say it's already made things easier in Haskell.

How long did it take for calculus to make things easier for most people?