If you've already got DateTime objects, then you should use their methods to do all your date/time math, and not be working with regexes or manual date/time math. To turn a string into a DateTime object, I like DateTime::Format::Strptime. Note that you need to supply the correct time zone to DateTime::Format::Strptime for the comparison to work, and also that subtract_datetime_absolute is "the only way to accurately measure the absolute amount of time between two datetimes, since units larger than a second do not represent a fixed number of seconds." (Although in this case that level of accuracy might not be needed, and regular DateTime::Duration calculations might be enough.)

use warnings;
use strict;
use DateTime::Format::Strptime;

my $now = DateTime->now;
print "$now\n";

my $strp = DateTime::Format::Strptime->new(on_error=>'croak',
    pattern => '%Y-%m-%d %H:%M:%S', time_zone=>'UTC');
my $dtevent = $strp->parse_datetime('2017-06-28 05:30:31');
print "$dtevent\n";

my $diff_sec = $now->subtract_datetime_absolute($dtevent)
    ->in_units('seconds');
my $diff_hours = $diff_sec/(60*60);
print "$diff_sec s / $diff_hours h\n";

if ($diff_hours>2) {
    print "$dtevent was more than 2 hours ago\n";
}
[download]