If the allergy is severe, you'll see a reaction right away -- usually hives, swelling, or trouble breathing.
However, allergies don't always start off severe. The reaction could be mild at first -- so watch out over the next day or two see if there's any irritability, discomfort, rash, etc.
But
if there's a reaction, however mild, be very, very careful. Allergies, particularly these kinds of allergies, tend to get progressively worse with each exposure. So a reaction of slight redness today can turn deadly during the next exposure.
In a child that has no known allergies with no family history of allergies, I wouldn't be so concerned about the sandwich if there was no apparent reaction. But, since your child already has known allergies, he's at greater risk of being allergic to other things and watching him for an ever-so-slight reaction is probably the best thing to do. And then the RAST testing will definitely help with that, too.
If you didn't notice anything after an hour, I say it's okay to put him to bed. If he had a moderate or severe reaction, you'd definitely know by now. But I'd definitely hold of on another exposure (as best you can, of course) until after the results of the RAST. And if you notice a mild reaction tomorrow, then definitely mention that to his allergist!
