This was really interesting!
About 2.4 billion people -- 30% of humans -- live within 100km of the ocean.
I think, for the rest of us, it's important to get to the coasts even if it's not convenient.
For me, my answer is about a month; I was on the shore in Carlsbad CA about 3 weeks ago. I probably won't see the ocean for another 3-6 months, though!
@jonn Wikipedia says "The Baltic Sea is an arm of the Atlantic Ocean"
https://en.wikipedia.org/wiki/Baltic_Sea?wprov=sfla1