> "Startups are a long-term game. My best advice is to treat entrepreneurship as a career path, but it is easier said than done absent some amount of success. For me, I had a taste of it three years in and some real success six years in."
http://www.gabrielweinberg.com/blog/2013/05/on-the-cusp-of-something-big.html

For this sentence: "I had a taste of it three years in and some real success six years in." Could anyone explain to me how the grammar of "in" works here? Thanks!