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

my $ts1 = '2000-01-01 00:00:00.000000';
my $ts2 = '2009-03-05 18:59:11.674653';

my $elapsed = time_diff($ts1, $ts2);
sub time_diff {
    my ($ts1, $ts2) = @_;
    my ($yr1, $mon1, $day1, $hr1, $min1, $sec1) = unpack('A4xA2xA2xA2x
+A2xA2', $ts1);
    --$mon1;
    my $micro = substr($ts1, 19);
    my $epoch1 = timelocal($sec1, $min1, $hr1, $day1, $mon1, $yr1);
    $epoch1 += $micro;
    my ($yr2, $mon2, $day2, $hr2, $min2, $sec2) = unpack('A4xA2xA2xA2x
+A2xA2', $ts2);
    --$mon2;
    $micro = substr($ts2, 29);
    my $epoch2 = timelocal($sec2, $min2, $hr2, $day2, $mon2, $yr2);
    $epoch2 += $micro;
    return $epoch2 - $epoch1;
}
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Date::Time: "This module does not parse dates! ... Instead, take a look at the various DateTime::Format::* modules on CPAN."

A suitable candidate in this case would be DateTime::Format::DateParse: "This module is a compatibility wrapper around Date::Parse."

So just use Date::Parse. The first two lines of a three line synopsis:

use Date::Parse;
        
$time = str2time($date);
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Neither does Time::Local, but it didn't stop him from doing his own parsing. Do you really need a module to replace a regex match or

my ($Y,$M,$D, $h,$m,$s) = unpack('A4xA2xA2xA2xA2xA2', $time_str);
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From that, you can contruct a DateTime object and do date and time arithmetic.

That said, I don't see the need to replace Time::Local with DateTime here. It seems to me that L~R made appropriate and maximal use of modules. Now, if you wanted the answer to be of the form X days, Y Hours and Z Seconds, DateTime is your man!

#!/usr/bin/perl
#seconds to #d_HH:MM:SS.ss and back.

#constants
my $m = 60;
my $h = 60 * $m;
my $d = 24 * $h;

#example
print s2dhms(86000),"\n";
print dhms2s('23:53:20'),"\n";


sub dhms2s {
       my $dhms = shift;
       my @dinfo = split /d_|:/, $dhms;
       my ($s, $m, $h, $d) = reverse @dinfo;
       $d ||= 0;
       $h ||= 0;
       $m ||= 0;
       return (
         (( $d * 24  + $h ) * 60  + $m ) * 60  + $s
       );
}

sub s2dhms {
       my $secs = shift;
       my $D = int($secs / $d); $secs = $secs - $D * $d;
       my $H = int($secs / $h); $secs = $secs - $H * $h;
       my $M = int($secs / $m); $secs = $secs - $M * $m;
       my $S = $secs ;
       my $r;
       if ($D) {
               $r .= sprintf "%dd_", $D;
       }
       if ( $S == int $S ) {
               $r .= sprintf "%02d:%02d:%02d", $H, $M, $S;
       } else {
               $r .= sprintf "%02d:%02d:%05.2f", $H, $M, $S;
       }
       return $r;
}
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