How long must you live in a country before you can say you're "from" there?

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I am especially interested in what ex-patriates think about this question. The idea of where people are "from" is fluid. What do you think makes a country "yours"? Do you think that there is a certain amount of months or years you have to live in a country before you consider it home? What kind of responses have you had from friends/family/other communities when they agreed or disagreed?