There is a distinction between a snap judgement about a person, and a prejudice held against that person. The former is made in the first moments of meeting; the latter needs to be formed before meeting to be a genuine prejudice. This distinction matters because whereas prejudice is unacceptable, snap judgements seem to be the psychological norm.
Empirical work by a pair of psychologists, Alexander Todorov and Janine Willis, ten years ago at Princeton University established two things: that “first impressions” take about a tenth of a second to form, and that they are hard to efface thereafter. For the person about to have a job interview, this is rather daunting news. But is not just employment prospects that turn on first impressions: social and romantic prospects hinge on them too.