"I need to parse through the array and take teh time of the first Event A, and then find the first Event B after Event A, and calculate the time delta."

And then what? Do you look for the next Event A and use it as the base to find the delta against the next Event B or do you go all the way back to the 2nd Event A that you found in the first iteration? All the answers given so far seem to pick the later, but i'm choosing the former and providing a solution that uses a hash. :) Hope this helps!

use strict;
use warnings;

my %h;
while (<DATA>) {
    chomp;
    ($a,$b) = split;
    if ($a eq 'a') {
        $h{a} ||= $b;
    } elsif ($a eq 'b') {
        print $b - $h{a}, $/;
        %h = ();
    }
}

__DATA__
a 123
a 125
b 127
a 129
a 130
b 131
a 132
b 133
[download]

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)