How long should I wait for the interviewer to get in touch?
Not getting a follow-up call, as promised, happens more than you think. Candidates are sure they are a certainty for the position, they're expecting an offer. Then, they hear nothing. This is not only frustrating for the candidate, but reflects poorly on the company.
If after a Monday interview you were told that a decision would be made before the end of the week, by Friday you'll be having doubts if there has been no call from the company. Does this mean you're not going to get an offer? Should you call to find out what's up. Or, should she just wait until after the weekend?
The fact is you have no idea why they haven't called, but you should hold your guns for a few more days before getting in touch. There may have been a crisis in the company and they may have a very valid reason for not calling you as promised. Of course its common courtesy for them to get in touch to let you know the decision is being delayed, but companies aren't always concerned about what the most courteous thing to do is.
If you don't get a return call as promised, call them and leave a message. Be prepared, professional and courteous. Try to reach the person at least once, explaining you want the information before you consider other positions because this company is your first choice. If you don't get an answer, forget about it. There is a fine line between being persistent and being a pest, and do you really want to work for a company that won't return your calls?
You may get lucky and actually reach the person when you call. If you do have such luck, use this opportunity to ask for feedback on your interview. Sometimes, not often, a person will take the time to give you advice. If this happens, be grateful and learn from the experience.
Most employers are aware that candidates are anxious about the status of their acceptance, and will let them know in a timely manner. But, there are employers who do keep candidates waiting and wondering what happened, even though they said they would call by a certain date.
In the meantime, rather than sitting and waiting for a phone call that may never come, continue to work on your job search. It is never wise to put all your eggs in one basket.