Here's something that I think does what you want. As a bonus I've made it strict-clean too.

The changes are all in the data loading code. Each individual record that you were building was an array of one element (and that element was a reference to the hash that you really wanted). This didn't break because Perl was trying to interpret it as a pseudo-hash (does anyone else think that pseudo-hashes cause more problems than they solve?)

Anyway, by simply removing the extra array, it all seems to work now. You could probably clean it up a bit more, but I was going for the least number of changes to your original script.

use strict;

my %ID;

#load the data...
while (<DATA>) {
  chomp;
  my @result = split (/\|/);
  my $rec = {LastName=>$result[1], FirstName=>$result[2], 
         TimeIN=>$result[3], TimeOUT=>$result[4]};
  push @{$ID{$result[0]}}, $rec;
}

#print the data
foreach my $key(sort keys %ID){
  print "$key\n";
  foreach (@{$ID{$key}}){
    print "$_->{LastName}\n";
  }
}

__DATA__
0001|Flintstone|Fred|0900|1300
0001|Flintstone|Fred|0900|1100
0001|Flintstone|Fred|1200|1630
0002|Flintstone|Wilma|0900|1500
0002|Flintstone|Fred|0930|1100
0003|Rubble|Barney|0900|1100
[download]

--
<http://www.dave.org.uk>

European Perl Conference - Sept 22/24 2000, ICA, London
<http://www.yapc.org/Europe/>