title: Most efficient way to convert a ISO Date into Unix timestamp?
body: <p>In my application, I have some records which I need to filter based on some time parameters. To do the date comparisons, I need to convert the dates in my records (a string in the format YYYY-MM-DD), to a unix timestamp (seconds since 1970). Since I have many thousands of records, I really want to find the most efficient way to do it.</p>
  
  <p>Answers to <a href="https://stackoverflow.com/questions/455554/datetime-to-unix-timestamp">another question</a> suggested doing it in the database (not an option here, sadly), using <code>strtotime()</code> or <code>strptime()</code>, but these don't <em>feel</em> like the most memory- and time-efficient methods, you know?</p>
  
  <p>Given that I know the exact format of my input, would perhaps using some form of string manipulation (<code>substr</code>, or <code>explode</code>) combined with <code>mktime</code> be better?</p>
  
  <p><em>If you believe I'm being premature in my optimisation, then just humour me ok?</em></p>