First, your split creates a couple of empty fields caused by the double colons present. Secondly, the "hh" is still part of "123-456 hh", is this intentional?

If you want to stick to split, you could re-join hh with mm afterwards:

use strict;
use warnings;
use Data::Dumper;
my $line = "A::B:123-456 hh:mm:C::D:789";
my @array = split /:/, $line;
print Dumper \@array;
splice @array, 3, 2, join( ":", @array[ 3..4 ] ) ;
print Dumper \@array;
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