Apostrophe query - when something is going to happen in the future.

[BroccoliSpears]

In a months time?

In a month's time?

In a months' time?

I don't really think it's the third one, I only included it for completeness. But does the time belong to the month? And does that mean the second one is right?

2nd - month is singular and it is possessive, "in two months' time" for the plural

In a month's time. Or in three months' time.

Excellent. Thank you.

viz. "Two Weeks' Notice", which should have been the correct title of the film for which Lynne Truss went round defacing posters.