Mean time = average time ?

Since many have a biphasic reaction within 2 hours.....that means many could be beyond 8 hours.

Yes, mean = average.  The report states the study group had biphasic reactions from 1 to 72 hours after the initial reaction.  S.C.A.R.Y!!

My phase 2 reaction was pretty scary too, although not quite as frightening as some of yours.   

DD's worst reaction (at age 7) was probably bi-phasic, but we're still stumped as to when the initial reaction started.

Lunch at school ~11:00 a.m.
One hive on chest ~3:00 p.m. (unsure if she had any symptoms prior since she was in school)
Spreading rash/tiny hives ~6:00 p.m.
Full blown anaphylaxis with breathing difficulty ~8:00 (nothing to eat since lunch and a bag of Fritos after school - only confirmed allergy SF) received Epi and Benadryl by me and then IV Pepcid and steroids at the hospital
Grade V anaphylaxis including respiratory arrest, cardiac arrest and LOC ~10:00 p.m.

And now I'm shaking and feel like I want to puke. 

The most overtly horrifying reaction DD ever had was a biphasic phase II at 2yo.

time to onset was 4 hr on the dot from the initial reaction, which was so non-specific as to not be fully recognizable as "allergic" in nature.


The late phase was unbelievably fast (seconds to full anaphylaxis) and I still have trouble wrapping my head around how severe that reaction was-- it was hard to tell whether DD was choking on mucous or if her airways were that swollen... but she was COVERED with hives-on-top-of-hives, vomiting, and then... more ominously, barely conscious.   

I've never-- ever-- been so glad to live 90s from the emergency room doors.  NEVER.  Longest car ride of my life.

We've also seen biphasics from allergy shots-- those tended to be 8hr on the nose.  It was so predictable that for a while, our allergist had us on his "call in the morning" list the day after an allergy injection.    (I  him so much.)

Overall frequency of biphasic reactions was 7.36% of anaphylactic reactions with prospective studies reporting a frequency of 9.07%. Mean time to the second phase of BA was 8.13 hours (95% CI, 6.13-10.14) with similar times between both pediatric and adult populations.

The stuff nightmares are made of.