Sometimes the words for exact periods of time are also used to talk about approximate periods of time. Usually, this kind of phrase emphasizes how long something is taking. At this rate itll take weeks to finish the project (= it will take too long). Hes been doing the same job for years and years (= a very long time).
Other phrases used for talking about how long something takes
Youre late Ive been waiting (for) ages!
Ive had these boots for quite a while.
Will the builders be here long? Yes, they only started a short time ago.
Shell be here in a second/moment/minute.
Would you mind waiting a minute? Ill be with you presently/shortly.
Periods of time in the past and present
These phrases are used to talk in a general way about time in the past or in the present:
Punk music was popular in the late 1970s and early 80s.
Our house was built in the mid-sixties.
The hospital dates from the turn of the century (= the beginning of the century).
Electric lights were invented near the end of the nineteenth century.
Greek civilization was one of the most important in ancient times.
Medical science has developed enormously in modern times.
I love to hear Grandpa talk about the old days (= the time when he was young).
In those days it was very difficult to travel across Africa.
Everyone seems to be on the Internet nowadays/these days.
Im really busy with work at the moment.
A period of time from one point of time to another point
Here are some common ways of saying this:
We stayed in Brussels from Thursday to Monday.
Its open from nine oclock until/till half past five.
(US): The performances are Monday through/thru Friday (= they are on Monday, Tuesday,Wednesday, Thursday and Friday).