Since str2time() is a relatively expensive routine, this a perfect time for pulling out the "Orcish Maneuver".

In the example above, change   my @sorted = sort {str2time($a) <=> str2time($b)} @dates; to

  my %cache;
  my @sorted = sort {($cache{$a} ||= str2time($a)) <=>
                     ($cache{$b} ||= str2time($b)) } @dates;
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