I'd forego the ST, and use a GRT instead:

@s =
  map { (my $x = join '', reverse /(..)\s*(.*)/) =~ s/00:/12:/; $x }
  sort
  map { (my $x = sprintf "%2s%5s", reverse /(.{4,5})(..)/) =~ s/12:/00
+:/; $x }
  @t;
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japhy -- Perl and Regex Hacker