$ cat test.pl
use strict;
use warnings;

sub timestamp
{
    my @st = localtime (shift);
    return sprintf "%04d-%02d-%02dT%02d:%02d:%02d.000-0700",
        $st[5] + 1900, ++$st[4], @st[3,2,1,0];
    }

sub starttimestamp  { return timestamp (time);             }
sub endtimestamp    { return timestamp (time + (15 * 60)); }
sub futuretimestamp { return timestamp (time + shift);     }

my $fts = futuretimestamp (162 * 60 * 60); # Stamp 162 hours ahead
print $fts, "\n";
$ perl-all test.pl
=== base/perl5.6.2	5.006002 i686-linux-64int-perlio
2013-12-02T06:46:51.000-0700
=== base/tperl5.6.2	5.006002 i686-linux-thread-multi-64int-ld-perlio
2013-12-02T06:46:52.000-0700
=== base/perl5.8.8	5.008008 i686-linux-64int
2013-12-02T06:46:56.000-0700
=== base/tperl5.8.8	5.008008 i686-linux-thread-multi-64int-ld
2013-12-02T06:46:56.000-0700
=== base/perl5.8.9	5.008009 i686-linux-64int
2013-12-02T06:46:56.000-0700
=== base/tperl5.8.9	5.008009 i686-linux-thread-multi-64int-ld
2013-12-02T06:46:57.000-0700
=== base/perl5.10.1	5.010001 i686-linux-64int
2013-12-02T06:46:58.000-0700
=== base/tperl5.10.1	5.010001 i686-linux-thread-multi-64int-ld
2013-12-02T06:46:58.000-0700
=== base/perl5.12.5	5.012005 i686-linux-64int
2013-12-02T06:47:05.000-0700
=== base/tperl5.12.5	5.012005 i686-linux-thread-multi-64int-ld
2013-12-02T06:47:05.000-0700
=== base/cperl5.14.4	5.014004 i686-linux-64int-ld
2013-12-02T06:47:15.000-0700
=== base/perl5.14.4	5.014004 i686-linux-64int
2013-12-02T06:47:16.000-0700
=== base/tperl5.14.4	5.014004 i686-linux-thread-multi-64int-ld
2013-12-02T06:47:16.000-0700
=== base/cperl5.16.3	5.016003 i686-linux-64int-ld
2013-12-02T06:47:25.000-0700
=== base/perl5.16.3	5.016003 i686-linux-64int
2013-12-02T06:47:25.000-0700
=== base/tperl5.16.3	5.016003 i686-linux-thread-multi-64int-ld
2013-12-02T06:47:26.000-0700
=== base/cperl5.18.2	5.018002 i686-linux-64int-ld
2013-12-02T06:47:36.000-0700
=== base/perl5.18.2	5.018002 i686-linux-64int
2013-12-02T06:47:37.000-0700
=== base/tperl5.18.2	5.018002 i686-linux-thread-multi-64int-ld
2013-12-02T06:47:37.000-0700