If you're going to dust this one off, you could also mention the standard optimisation:

 my $yesterdays_date = localtime;
 sleep 86400;
 print "Yesterday, it was $yesterdays_date\n";
 sleep -86400;
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Yes, yes, I know it's sad...

Update: Can't claim credit... I believe that belong to Ilya Zakharevich, otherwise it would have been even sadder, and I wouldn't've dared post.