So 1 year -> 2 decades?

Yes.

Note that this also comes out about the same if you're using months (12 months -> 24 years (2.4 decades)) and (at least within a factor of two-ish) weeks (52 weeks -> 104 months (0.867 decades).

I'm not claiming this is accurate, I'm stating that it's a heuristic I'm familiar with.

This may have been in Arthur Bloch's Murphy's Law and Other Reasons Things Go Wrong, though I'm not finding it in comparable collections. Possibly from project planning literature I was reading in the 1990s (DeMarco & Lister, Brooks, Boehm, McConnell, etc.).