Remember, it is for information as you investigate a particular field. You only want information. You are interested in that field. Indicate that you would like to speak for approximately 20 or 30 minutes with a person in the area of particular interest to you. Don't be surprised if the interview lasts an hour.
People like to be helpful and enjoy talking about themselves.
Allow at least one hour between interviews. Frequently, they last longer than you expect and travel time must be figured. Since you are interviewing for information only, use this opportunity to learn as much as you can about particular occupations. How you answer will depend on how far along you are in your job search. You may or may not be ready to commit yourself to a particular occupational field.