Can i have an allergic reaction to something i ate 12 hours later?

Delayed-type allergy: Allergy caused by blood cells that have become allergic to a chemical or food can often cause symptoms that are delayed for 6 to 24 hours after exposure.

Rare: Most food allergy occurs within 2 hours after although allergy to red meat may occurs as late as 6 hours. I recall having read a report noting that allergic reaction to wheat occurring as late as 12 hrs later but have not read any confirmation of this observation. Thus in general it is a "no".