my $previous = "";

# skip $item variable
# 'for' just looks funny in this use
foreach (@list) {
  # regex once instead of twice 
  # no extra work shuffling $previous back and forth until needed
  if (m/^(.+)\: .+/ and $1 ne $previous) {
     $previous = $1;

     # take the sleep hit on the first item to save time later
     # (maybe even 5 seconds worth if you have a lot of items)
     sleep(5);
  }
  print $_;
}