use DateTime;
my $source = DateTime->new(year => 2007, 
                           month  => 7,  
                           day => 2, 
                           hour => 13,   
                           minute => 55, 
                        time_zone => 'America/Los_Angeles');
my $result = $source->clone()
                    ->set_time_zone('Asia/Calcutta');
print $source->strftime("%F %r %Z"), "will become ", 
      $result->strftime("%F %r %Z");