To say how soon something will happen the expression "in...'s time" is used. So, "It'll be done in a week's time (sing. poss.) or in two weeks' time (plu. poss.)." Only one out of 47 got it right? Jeez! What's happening to our language? Doesn't anyone out there know how to use it correctly anymore?
When a noun comes as an adjective, we use the singular form of that noun.
Ten dollar note
six month course etc.
So? What's your point, Wilson?
Many people answering are learners, so that can be reflected in the results. Give it time and things will change.
I am happy to flow you new idoim words
Don't keep us confused. Please provide correct answer too.