advance notice

[six6]

what is the different between them?

7-day advance notice
7 day advance notice
7 days advance notice
7 days' advance notice

Thanks!

[BobK]

What is the difference. They all use 'advance' unnecessarily. The last is best, as it means 'notice [of] seven days' [extent/duration/<whatever>'. The third is common, though, and I wouldn't call it wrong.

Your list omits another variant '7-days' notice'; this is often used in Br Eng (less so, I think, in Am E). The hyphen shows that '7-days'' is being used adjectivally (as it's not in my first para.)

b