#!/usr/bin/env perl

use 5.014;
use warnings;

$_ = <DATA>; chomp;

/^  (?<mon>\w+)\s(?<dd>\d\d)
 \s (?<time>..:..:..) # could capture hh:mm:ss separately if need be
 \s (?<src>\d+\.\d+\.\d+\.\d+)
 # keep going with your sub-expressions
/x;

say "time: $+{time}  src: $+{src}";

__DATA__
May 20 18:57:27 1.23.25.5 %ASA-6-106100 a6 [local4.info] access-list Myaccess-Block permitted tcp outside/10.31.0.9(3803) -> inside/10.29.10.91(4127) hit-cnt 1 300-second interval [0xa178b29d, 0x0]


##</code><code>##

    my $IP_ADDR = qr/\d+\.\d+\.\d+\.\d+/;
    /...(?<src>$IP_ADDR).../