"A few hours's time, or a few hours' time?"

Hi All,
I'm looking to help settle a gentlemen's challenge - my colleague is saying that this phrase is correct: "Our hope is that in a few hours’s time", citing Strunk & White's Rule II. I'm citing rules of inanimate possessives, where pluralized nouns get the apostrophe "post plural".

Please help settle this - we're relying on your expertise to help! Thanks!