#!/usr/bin/perl
use v5.14;

my $input_line = 'T 1310234540 19<24SomeUserName>19 This is user chat. ';

$input_line =~ m/
    \<      # after the '<' sign, and
    \d+     # any digits that follow it,
    (\w+)   # capture all letters as $1
    \>      # then expect the '>' sign
    \d+\s+  # followed by some other digits and whitespace
    (.+)    # everything that follows is the message
/x;

my $username = $1;
my $message  = $2;

say "Username: [$username], Message: [$message]";