What is the incubation period for the flu(USA Today-CDC)?
<>conducted a question and answer session with the acting director of the Center for Disease Control, Richard Besser and Martin Blaser, former president of the Infectious Disease Society of America. Here is the relevant text from that discussion, as answered by Martin Blaser:

Q: What is the incubation period for the flu?

A: In most cases, infected people develop symptoms within one to four days, Blaser says.

You can read all of the questions and answers at the link below.