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.)
- For Teachers