in reply to sort based on date

You have made a fine application of the Schwartzian Transform. The only speed improvement I can think of is replacing the ParseDateString-function by something with less overhead (perhaps a regex made specifically for this format of dates).

CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

In Section Seekers of Perl Wisdom