use strict; use warnings; use feature 'say';
use DateTime::Format::Strptime;

my $parser = DateTime::Format::Strptime->new(
    pattern => '%F %T',
);

my $now = DateTime->now->hour;
my $evt = $parser->parse_datetime('2017-06-15 13:14:31')->hour;
my $diff = $now - $evt;

say "now: $now";
say "evt: $evt";
say "diff: $diff";

__END__

##</code><code>##

$ perl 1193762.pl
now: 7
evt: 13
diff: -6