#! perl -slw
use strict;
use Data::Dumper;

sub hm2mins{ 
    $_[ 0 ] =~ m[^(\d\d):(\d\d)$] and return $1 * 60 + $2;
}
sub mins2hm{ 
    sprintf '%02d:%02d',  int( $_[ 0 ] / 60 ), $_[ 0 ] % 60  ;
}

my @HM = (
  [ '03:30', '05:45' ],
  [ '05:45', '09:15' ],
  [ '10:00', '11:35' ],
  [ '11:00', '15:40' ]
);

my $stick = '0' x ( 60 * 24 );

for ( @HM ) {
    my( $start, $stop )  = ( hm2mins( $_->[ 0 ] ), hm2mins( $_->[ 1 ] 
+) );
    substr( $stick, $start, $stop - $start ) = '1' x ( $stop - $start)
+;
}

my @out;
push @out, [ pos( $stick ), length $1 ] while $stick =~ m[(0+)]g;

@out = map{ 
    my $start = $_->[ 0 ] -  $_->[ 1 ];
    my $stop = $_->[ 0 ];
    [ mins2hm( $start ), mins2hm( $stop ) ]
} @out;

print Dumper \@out;

__END__
P:\test>341852
$VAR1 = [
          [
            '00:00',
            '03:30'
          ],
          [
            '09:15',
            '10:00'
          ],
          [
            '15:40',
            '24:00'
          ]
        ];
[download]