Hello! Searching has proven less fruitful than hoped, and the most successful searches ultimately just point to using DateTime. I like this idea, but the senior Perl devs in our company prefer I stick with Date::Manip.

First, a summary with results. I am in mountain time, constructing a date object, changing it to US/Pacific, then making more changes based on user-supplied datetime parameters. In most cases, things work beautifully, but when going more than 15 days back in time, bizarre behavior is occurring.

[me ~]$ perl datefail.pl --startday='-15 days' --endday='-14 days'
Start with Today
20151120T22:51-0700
Fix timezone
20151120T21:51-0800
Set the right day
20151105T21:51-0800
Strip the hours
20151105T00:51-0800
Strip the minutes
20151105T00:00-0800
[me ~]$ perl datefail.pl --startday='-19 days' --endday='-18 days'
Start with Today
20151120T22:51-0700
Fix timezone
20151120T21:51-0800
Set the right day
20151101T21:51-0800
Strip the hours
20151101T01:51-0700
Strip the minutes
20151101T01:00-0700
[download]

Enjoy this simplified code that illustrates the problem.

#!/usr/bin/perl

use strict;
use warnings;
use Date::Manip;
use Getopt::Long qw(GetOptions);

my $startDay;
my $endDay;

GetOptions(
        'startday=s' => \$startDay
        ,'endday=s' => \$endDay
);

my ( $startDDelta,$zeroStartH,$zeroStartHDelta,$zeroStartM,$zeroStartM
+Delta );

print "Start with Today\n";
my $dateObjStart = new Date::Manip::Date('now');
print $dateObjStart->printf('%Y%m%dT%H:%M%z') . "\n";

print "Fix timezone\n";
$dateObjStart->convert('US/Pacific');
print $dateObjStart->printf('%Y%m%dT%H:%M%z') . "\n";

print "Set the right day\n";
$startDDelta = new Date::Manip::Delta($startDay);
$dateObjStart = $dateObjStart->calc($startDDelta);
print $dateObjStart->printf('%Y%m%dT%H:%M%z') . "\n";

print "Strip the hours\n";
$zeroStartH = '-'.$dateObjStart->printf('%H').' hours';
$zeroStartHDelta = new Date::Manip::Delta($zeroStartH);
$dateObjStart = $dateObjStart->calc($zeroStartHDelta);
print $dateObjStart->printf('%Y%m%dT%H:%M%z') . "\n";

print "Strip the minutes\n";
$zeroStartM = '-'.$dateObjStart->printf('%M').' minutes';
$zeroStartMDelta = new Date::Manip::Delta($zeroStartM);
$dateObjStart = $dateObjStart->calc($zeroStartMDelta);
print $dateObjStart->printf('%Y%m%dT%H:%M%z') . "\n";
[download]

Thank you kindly for any suggestions you can offer that don't require me to refactor the code to use another package. (Though if that's the only option, I'll just offer the department their choice between that or, say, ColdFusion. Hah.)