Use of '' 's"
1) If we have classical name ending with "s" (e.g. James), we form genitive by adding apostrophe. When it's used in modern context, we add 's'
James' vs James's
2)'s is used to describe being at sb's place (at Jane's, at my grandmother's, house of Mary's)
3) When name is long , e.g. The elderly lady's house, John's and Mike's book.
4) Idiomatic expressions. NO RULES.
money's worth
hair's breadth
wine glass
committee meeting
church mouse
tea break
party politics
doll's house
TV licence etc.
(as far as period of time is concerned, we use apostrophe : 'day's journey', 'hour's work' etc)