my $TIMESTAMP;
...
for (@dates) {
     $TIMESTAMP = $_->[0]->strftime("%Y-%m-%d %R");
}

##</code><code>##

my $TIMESTAMP = $dates[-1][0]->strftime("%Y-%m-%d %R");

##</code><code>##

my @log_final;
my $last = 0;

while (my $log_line = $log_bckwards->readline) {
    if ($log_line =~ /$TIMESTAMP/) {
        $last = 1;
    }
    elsif ($last) {
        last;
    }
    unshift @log_final, $log_line;
}