In the Big Bang Theory,
You are early. The movie doesn't start for an hour.
Is he saying the movie doesn't start in an hour? Is the preposition "for" correct?
The movie doesn't start for an hour.
is the same as:
The movie starts in an hour.
The movie doesn't start until an hour from now.
The preposition for is used with a period of time.
ex. for an hour, for 2 days, for 3 months
But what the speaker is implying in this construction is that this is very or too early. It is correct in spoken English.