Аз съм учила английска граматика като академична дисциплина, защото уви, не съм носител на английския език. Там се обръща внимание именно на примерите, които давате и само на тях. Дори са представени като подтема към темата на изразяване на притежание. Става дума за устойчиви съчетания в редица изрази, едни от които са именно за период от време, какъвто пример посочвате. Е, не са чак толкова устойчиви, както правилно отбелязвате и Вие в постинга си, а се променят с времето - както всичко на този свят :) Ето примерна извадка на тази тема от учебник по английска граматика: A. The possessive case is chiefly used of people, countries or animals as shown above. It can also be used: 1. Of ships and boats: the ship's bell, the yacht's mast 2. Of planes, trains, cars and other vehicles, though here the of construction is safer: a glider's wings or the wings of a glider the train's heating system or the heating system of the train 3. In time expressions: a week's holiday, today's paper, tomorrow's weather, in two years' time, ten minutes' break two hours' delay, a ten-minute break, a two-hour delay are also possible: We have ten minutes' break/a ten-minute break. 4. In expressions of money + worth: £1's worth of stamps, ten dollars' worth of ice-cream 5. With for + noun + sake: for heaven's sake, for goodness' sake 6. In a few expressions such as: a stone's throw, journey's end, the water's edge 7. We can say either a winter's day or a winter day and a summer's day or a summer day, but we cannot make spring or autumn possessive, except when they are personified: Autumn's return. 8. Sometimes certain nouns can be used in the possessive case without the second noun. a/the baker's/butcher's/chemist's/florist's etc. can mean 'a/the baker's/butcher's etc. shop'. Similarly, a/the house agent's/travel agent's etc. (office) and the dentist's/doctor's/vet's (surgery): You can buy it at the chemist's. He's going to the dentist's, Names of the owners of some businesses can be used similarly: Sotheby's, Claridge's Some very well-known shops etc. call themselves by the possessive form and some drop the apostrophe: Foyles, Harrods. Names of people can sometimes be used similarly to mean '...'s house': We had lunch at Bill's. We met at Ann's.