For vs During

"For" indicates a period of time, the duration of an action or an event:

The boss was away for a week.

The play lasted for more than 3 hours.

We're going away for the weekend.

In questions and negatives with "long" it is often optional:

Will you stay (for) long?

How long did he sing (for)?

Oh. He didn't sing (for) long!

"During" is used with a noun/pronoun (or other noun form). It is used to express an event inside which an action takes place.

The bomb exploded during the film. (The film is the event, explode is the action)

John forgot his lines three times during the play. (The play is the event, forget is the action)

The revolution occured during the president's absence abroad. (Absence is the event, occur is the action)

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