Can anaphylaxis have a delayed onset?

Possibly: Anaphylaxis is a life threatening allergy reaction that occurs within minutes to hours of being exposed to the allergen in question. Very rarely one can see anaphylaxis that is delayed and not occur for a couple of hours after exposure. More commonly one sees anaphylaxis that occurs immediately then the symptoms recur hours later -- this is called a biphasic response.

Yes.: Delayed onset of anaphylaxis to beef has been described. Its referred to as alpha-gal allergy, occurs about 4 hours after a meal, and curiously develops after the bite of the lone star tick or the red chigger. This allergic reaction is to a small carbohydrate, Alpha galactose, and not as usually seen, to a protein. Most of these reactions have been reported in the south & in australia.