How long does an interview usually last according to the speaker?

Interview is extremely important if you want to apply for a job. To be successful in a job interview, you should demonstrate certain personal and professional qualifies to your potential bosses. (14[B]) (17[D])You need to a good image in a limited time, usually from 40 to 70 minutes. You must leave a positive impression which the interviewer will remember while he interviews other applicants.
     You should especially pay attention to some qualities during the interview. (15[C]) First of all, you should take care to appear properly dressed. The right clothes worn at the right time can win the respect of the interviewer and his confidence in your judgment. It may not be true that clothes make the man, but the first and last impression of yours is determined by the clothes you wear. That is what it means by "dress for success". (16[D]) Secondly, you should reflect confidence by speaking in a clear voice, loud enough to be heard without being aggressive. You should be prepared to talk knowledgeably about the position you’re applying for. Finally, to be really impressive, you must convey a sense of self-confidence and an enthusiasm for work. If you display these characteristics with just a little luck, you’ll certainly succeed in a typical personal interview.