A lot of Hiring Managers relied on initial impression and often made up their minds about a candidate during the first three minutes. The danger is that, when that initial impression is very strong, you could find yourself using the entire 20 minutes to validate that first impression. The interview then has a preprogrammed conclusion. As a result, you could miss valuable information.
Concentrate hard on NOT allowing that to happen.
Allow at least 20 minutes. The purpose of such a time is to get relevant information about the candidate regarding a number of issues:
• Competencies required for handling the work.
• Interest in doing the job.
• Ability to adjust to the work environment.
• Likelihood of being accepted by peers and superiors.
• Probability of remaining with the organization.
• Potential for growth and development.
• Ability to articulate well.
• Factors that might interfere with performance.
• Level of maturity.
• Clarity of judgment.
• Sense of self-management and control.
None of this can be accomplished if you have already allowed yourself to be programmed into an initial decision made. Use that first 20 minutes to listen actively. Encourage the candidate to provide you with as much quality information as possible. Any evaluation of what you hear must wait until the 20 minutes are complete. At the end of 20-minute time frame, you make a decision to continue the interview, if you believe that the candidate is viable, or to terminate the interview, if you think that the candidate and the job are not appropriate for one another.
If you determine that the candidate is viable, then you continue the interview for an additional 20 minutes. An efficient and productive interview of a suitable candidate, therefore, should take approximately 40 minutes. By the end of 40 minutes, you may not make a hiring decision, but you know with certainty what the candidate would bring to the organization in terms of strengths and weaknesses if he or she were hired.
Although a 40-minute interview should be sufficient to evaluate a professional, technical or executive candidate, it may well be overkill in terms of evaluating a clerical person. At that level, you might consider a 15-minute courtesy interview and 30 minutes for the total interview.
Source Rosenberg, DeAnne Hiring The Best Person For Every Job, 96-98 Wiley