I just used the phrase "a few months' hiatus". Here are some more examples of this construction:
What's going on here? What's with the apostrophes?
Welcome to the genitive case. The grammarian Charles Fries would say that these phrases are examples of the genitive of measure, but it seems to me that we use this genitive mostly with regard to duration. For instance, we don't say that baseball is "an inches' game", but we do say that home runs were "all in a day's work" for Babe Ruth. You can think of it as "the work of a day" (or "the war of a hundred years" or "a wait of a few minutes" or "a vacation of one week" or "a hiatus of a few months"). Just remove that "of", modify the word order, and add the apostrophe.
English is fun, eh?