The problem is in the truncate('to' => 'day') step. What you need is to truncate to "14th day", which is not that easy.

Do you think you can do with DateTime::Event::Recurrence or DateTime::Event::ICal? These modules provide a large set of recurrence modes.

#!/usr/bin/perl
use strict;
use warnings;
use DateTime::Event::Recurrence;

print "DateTime::Event::Recurrence: ", $/;

my $start = DateTime->today();
my $biweekly = DateTime::Event::Recurrence->daily(
    interval => 14,
    start    => $start,
);

print 'TESTING whether Date is in set...', $/;
my $date = DateTime->today();
print $biweekly->contains($date), ' ', $date->ymd, $/;
$date->add('days' => 7);
print $biweekly->contains($date), ' ', $date->ymd, $/;
$date->add('days' => 7);
print $biweekly->contains($date), ' ', $date->ymd, $/;
$date->add('days' => 7);
print $biweekly->contains($date), ' ', $date->ymd, $/;
$date->add('days' => 7);
print $biweekly->contains($date), ' ', $date->ymd, $/;
$date->add('days' => 7);
print $biweekly->contains($date), ' ', $date->ymd, $/;

[download]
output: 
DateTime::Event::Recurrence: 
TESTING whether Date is in set...
1 2013-05-15
0 2013-05-22
1 2013-05-29
0 2013-06-05
1 2013-06-12
0 2013-06-19

[download]

In reply to Re: Determine if a given DateTime is a member of a DateTime::Set by fglock
in thread Determine if a given DateTime is a member of a DateTime::Set by eibwen

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.