Onset is minutes to hours, usually within one or two hours of exposure. "In rare cases, anaphylaxis may be delayed for hours." (source https://www.mayoclinic.or

Onset is minutes to hours, usually within one or two hours of exposure. "In rare cases, anaphylaxis may be delayed for hours." (source https://www.mayoclinic.org/diseases-conditions/anaphylaxis/symptoms-causes/syc-20351468#symptoms https://www.mayoclinic.org/diseases-conditions/anaphylaxis/s...) Additionally: "anaphylactic reactions can also present in a biphasic manner in up to 20% of cases. Even after successful management of the initial presenting symptoms, there can be a recurrence of symptoms peaking 8 to 11 hours after the initial reaction." (source https://www.ncbi.nlm.nih.gov/books/NBK482124/ https://www.ncbi.nlm.nih.gov/books/NBK482124/)