Try this , it gave correct result of 20 minutes

#! /usr/bin/perl

use Date::Calc qw(Delta_DHMS);

($days, $hours, $minutes, $seconds) =
  Delta_DHMS( 2004,10,31,00,40,00,  # earlier
                2004,10,31,01,00,00); # later

print "$days days and - $hours:$minutes:$seconds \n";
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Neeraj