Here is a solution using Time::Piece.

C:\Old_Data\perlp>corelist Time::Piece

Time::Piece was first released with perl v5.9.5
[download]

#!/usr/bin/perl
use strict;
use warnings;
use Time::Piece;

my $dt = 'Jan 1, 2000 12:00:00';
my $fmt = '%b %d, %Y %H:%M:%S';

my $epoch = Time::Piece->strptime($dt, $fmt);

$epoch += 86400*5;

#print localtime($epoch)->strftime($fmt);
print $epoch->strftime($fmt);
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This prints Jan 06, 2000 12:00:00

Update: I wasn't sure if your question specifically wanted a DateTime solution or just a way to convert from a timestamp to epoch and back. Sorry if my post doesn't meet your expectations.

I'm not well acquainted with the DateTime module, but I'm sure there is a simple solution there as well.

Update2: Changed the print line to the desired form. Arrg