When talking about time or distance, we use the number + noun expression as part of a possessive compound noun.
If the number is one or less, or ends in a fraction: a half, a quarter, etc, the unit of measurement is in the singular and is followed by -‘s.
- One week’s break.
(number/One + unit of measurement in the singular/week + -s + noun/break)
(a break of one week) - It’s only half-an-hour’s drive.
(a drive of half an hour) - There’s half-a-metre’s width between the two walls.
(a width of half a metre)
If the number is more than one, the unit of measurement is in the plural and is followed by an apostrophe.
- It’s five hours’ drive from here.
(number/five + unit of measurement in the plural/hours + apostrophe + noun/drive)
(a drive of five hours) - We’ll be back in two weeks’ time.
(a time of two weeks) - It’s ten metres’ to the ground.
(a distance of ten metres to the ground)
