my $dt1 = DateTime->new( year => 2003, month => 5, day => 2,
                          hour => 7, minute => 53,
                          time_zone => 'Asia/Tokyo' );
 my $dt2 = DateTime->new( year => 2003, month => 5, day => 2,
                          hour => 5, minute => 53,
                          time_zone => 'Asia/Calcutta' );

 if ( $dt1 > $dt2 ) {
     ...
 } else {
     ...
 }

 $dt1->set_time_zone( 'Asia/Calcutta' );

 print $dt1->datetime, "\n";
 print $dt2->datetime, "\n";