Natural cortisol levels (your body's homemade steroids) are higher in the mornings and those levels taper off in late afternoon/evening. Steroids counteract allergies (to some extent), so I could see a relation between time of day and allergies based on that factor alone, for sure. It's one of the reasons my allergist recommends allergy shots first thing in the morning and won't give them beyond 1 PM. Most OIT protocols have similar time restrictions due to natural cortisol levels; and most food challenges are first thing in the morning as well for the same reason.
However, I'm not sure natural cortisol levels would have much of an effect over a severe systemic reaction. If you eat peanuts in the morning vs. late at night... and you have a severe and highly sensitive peanut allergy, you're going to be in serious trouble either way. But it may help somewhat; I am no expert.
Good luck finding the source of your reactions. I hope your allergist is following up with you often and giving you some direction on how to narrow down your search.