Print interviews can be very time consuming, and therefore, you need to make sure that you put aside a fair amount of time if you want to do it properly. Now the duration of a print interview can blow out for a number of reasons. Number one, a print reporter will tend to ask a lot more questions. Number two, the interview can be more relaxed than a television or radio interview, and therefore you may speak more freely and elaborate more. This takes time of course, and number three, you have a general off the record chat prior to the interview beginning. The reporter won't want to rush the interview.
They may be busy, but they'll also want to get as much information out of you as possible.