How Long Should a Phone Interview Be?
As a general rule, customer surveys should be as short as possible and still see the main goals of the survey.
For phone interviews, we recommend keeping the survey short enough so the average interview will take five minutes or less. We've found that customers are more likely to refuse the interview or hang up before the end if the call goes over five minutes.
The number of questions you can include in the interview will depend on the questions you're asking. Simple yes/no questions take very little time, while open-ended questions take longer but yield much richer insights. You should also try to avoid long introductions and explanations, since these not only take extra time, they often make the interview seem longer than it really is. We've found that a well-written interview can typically include 10-20 questions and stay under five minutes.