Thank you very much. I was so focused on getting the pack and sort working correctly that I completely overlooked that loop. For anyone who might be interested in doing something similar in the future, here is a stripped down version that works.
Once again, thanks everyone. 
#!/usr/bin/perl -w
use strict;
use Date::Calc qw(Mktime);

open (BIGLOG, "< D:/Logs/biglog.unsorted.log")
    || die "Cannot open unsorted log $!";

my( $offset, @index ) = 0;

while (<BIGLOG>){
    my $epoch = ( /^\s*#/ or /^\s\n/ or $_ !~ /^\s*\d/ ) 
        ? 0 
        : Mktime( unpack 'A4xA2xA2xA2xA2xA2', $_  );
    push @index, pack 'NN', $epoch, $offset;
    $offset = tell BIGLOG;
}

@index = sort {$a cmp $b} @index;

open (OUTFILE, "> D:/Logs/biglog.sorted.log") || die "Cannot write sor
+ted log $!";

while (@index){
    print OUTFILE readline_n(\*BIGLOG, shift @index);
}

close BIGLOG;
close OUTFILE;
exit;

sub readline_n{ 
    my( $fh, $line) = @_; 
    seek ($fh, unpack( 'N',substr( $line, 4, 4 )), 0) || warn "Problem
+ seeking to $line $!\n";
    scalar <$fh> 
}

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In reply to Re^8: Sort big text file - byte offset - 50% there (Added code) by msalerno
in thread Sort big text file - byte offset - 50% there by msalerno

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