We use in to say how long it takes someone to do something:
He was such a clever musician. He could learn a song in about five minutes.
We use an apostrophe -s construction (in a year’s time, in two months’ time) to say when something will happen. We don’t use it to say how long someone takes to do something:
I won’t say goodbye because we’ll be seeing each other again in three days’ time. We can also say in three days, without time, in this example.
He ran the marathon in six hours and 20 minutes.
Not: He ran the marathon in six hours and 20 minutes’ time.
in:- during a period of time
in the 18th century
in the fall
in the morning/afternoon/evening
I'm getting forgetful in my old age.
in:- after a particular length of time
to return in a few minutes/hours/days/months.
It will be ready in a week's time (= one week from now).
She learnt to drive in three weeks (= after three weeks she could drive).
so, Does Cambridge Grammar mean?
He could learn a song in about five minutes.=He could learn a song during about five minutes.?
we’ll be seeing each other again in three days’ time= we’ll be seeing each other again after three days?
So, "in 5 minutes" means either "during 5 minutes" or "after 5 minutes" right?