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If you find yourself in a situation where rescheduling an already planned job interview is necessary, it's important to communicate with your interviewer. Proactivity can be essential for a good impression, and sending a message explaining the need for change means the employer will be aware of the issue. Even if there are only potential circumstances arising that could end up requiring a date change, it’s best not to wait until the last minute – if changes do arise and there is no prior communication about them, the interviewer may be considerably more displeased.
Letting an employer know kindly of any potential delays has a positive side, too, as it allows them plenty of time to plan accordingly and alert their team of any forthcoming alterations. It demonstrates responsibility and understanding on behalf of you - the applicant - that such advanced notice can help the organization plan their schedule; in addition to that, such polite behavior leaves your name positively in their minds regardless of whether or not they rebook an alternative day for interviewing you.
More info: Importance of Background Checks