Hyphen Instead of Apostrophe When Time/Amount Adjective Is Said Without the S
The Apostrophe
Rulebase Summary
When a direct adjective construction involving time, value, distance, or amount is said with the s, use the apostrophe form (one week's vacation, two weeks' vacation). When the same construction is said without the s, use a hyphen instead and add an article like 'a' in front (a one-week vacation, a two-week vacation). The punctuation is based solely on the presence or absence of the s.
Examples
A. We took a two week's vacation after the trial.
A. We took a two-week vacation after the trial.
Said without the s — use hyphen, not apostrophe.
A. There was 20 minutes delay before the next session.
A. There was 20 minutes' delay before the next session.
Said with the s — use apostrophe for the plural possessive form.
Transcript Notes
The distinction between apostrophe and hyphen depends entirely on whether the s is present. Both forms are correct — each applies to a different construction. When the s is absent and a hyphen is used, an article (a, an) is typically added before the adjective.
Style Guide References (1)
BGGP