Phrasing "An hour's rest"

I was just posting a question to the Homebrewing StackExchange, and I found myself pondering the proper way to express my sentiment.

I first wrote "an hour's rest", but upon review, I deemed the apostrophe extraneous. What is the proper way to form this phrase? I can't make a case for the word 'hour' being plural or possessive, so I'm beginning to think the whole letter 's' is unnecessary.

Thoughts, anyone?

Solution 1:

This is what the Chicago Manual of Style terms an "idiomatic shorthand form of an of-phrase:"

an hour's delay is equivalent to a delay of one hour, or a one-hour delay

So: an hour's rest can be phrased as a one-hour rest. (I find a rest of one hour a bit stilted...)

Edit: As noted in my comment, in this idiom, delay or rest "belongs" to hour (it's of one hour), so it's "an hour's delay."

Solution 2:

I've always seen it with the apostrophe. Without would look goofy. Wikipedia has an explanation as to why (not that it's a standard grammar reference but I believe in this case it's correct):

An apostrophe is used in time and money references, among others, in constructions such as one hour's respite, two weeks' holiday, a dollar's worth, five pounds' worth, one mile's drive from here. This is like an ordinary possessive use. For example, one hour's respite means a respite of one hour (exactly as the cat's whiskers means the whiskers of the cat). Exceptions are accounted for in the same way: three months pregnant (in modern usage, we do not say pregnant of three months, nor one month(')s pregnant).