We use during to say when something happens, if it happens in or over a period of time. We use for to talk about the length of time something lasts.
She phoned me during the week to tell me that she was getting married. (referring to a point in the week)
We were in the cinema for three and a half hours.
Not: … during three and a half hours.
Our flight to New York was delayed for seven hours.
Not: … during seven hours.
We went to Italy for a week.
Not: … during a week.
We can also use for to refer to public holidays and seasons:
He always goes to his mother’s house for New Year.
Not: … during New Year.