I modified your script, so that it outputs a little more information: 
use strict;
use warnings;
use Time::Piece;

my $ctime = Time::Piece->new;
my $oldtime = Time::Piece->strptime('Dec 19 17:44:00 2016', '%b %d %T 
+%Y');

$oldtime = $oldtime - $ctime->tzoffset;

sub showtime { shift->strftime }

print "The current time is ", showtime($ctime), "\n";
print "The old time is ", showtime($oldtime + $ctime->tzoffset), "\n";

my $halfago = $ctime - 1800;

print "Half an hour ago is ", showtime($halfago), "\n";

if ($oldtime > $halfago)
{
    print "Old time is within a half hour\n";
}
else
{
    print "Old time is outside a half hour\n";
}

[download]
The parameterless form of Time::Piece's strftime includes time zone name. My output was: 
The current time is Di, 20 Dez 2016 10:09:19 Mitteleuropäische Zeit
The old time is Mo, 19 Dez 2016 17:44:00 UTC
Half an hour ago is Di, 20 Dez 2016 09:39:19 Mitteleuropäische Zeit
Old time is outside a half hour

[download]
Of course, since I didn't update $halfgo, it is really outside, but it illustrates davido's point.

In reply to Re^5: Simple (I thought) time comparison? by soonix
in thread Simple (I thought) time comparison? by sjessie

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