title: Adding days to a timestamp
body: <p>Giving a starting date, I'm adding four times seven days to get 5 different dates separated exactly a week each one.</p>
  
  <pre><code>//$date = '28-10-2010';
  $timestamp = mktime( 0, 0, 0, 10, 01, 2010 );
  echo "Date=".date( 'd-m-Y', $timestamp )."&lt;br&gt;";
  
  $timestamp += (60*60*24*7);
  echo "Date=".date( 'd-m-Y', $timestamp )."&lt;br&gt;";
  
  $timestamp += (60*60*24*7);
  echo "Date=".date( 'd-m-Y', $timestamp )."&lt;br&gt;";
  
  $timestamp += (60*60*24*7);
  echo "Date=".date( 'd-m-Y', $timestamp )."&lt;br&gt;";
  
  $timestamp += (60*60*24*7);
  echo "Date=".date( 'd-m-Y', $timestamp )."&lt;br&gt;";
  </code></pre>
  
  <p>The code outputs this:</p>
  
  <pre><code>Date=01-10-2010 Friday
  Date=08-10-2010 Friday
  Date=15-10-2010 Friday
  Date=22-10-2010 Friday
  Date=29-10-2010 Friday
  </code></pre>
  
  <p>Which as long as I know it's correct.
  But, see what happens when going through the 2010-10-31 and 2010-11-01</p>
  
  <p>$timestamp = mktime( 0, 0, 0, 10, 28, 2010 );
     [...]</p>
  
  <p>Curiously it outputs this:</p>
  
  <pre><code>Date=28-10-2010 Thursday
  Date=03-11-2010 Wednesday
  Date=10-11-2010 Wednesday
  Date=17-11-2010 Wednesday
  Date=24-11-2010 Wednesday
  </code></pre>
  
  <p>What's happening? Second date should be 04-11-2010!
  Also, I saw that this "fail" happens every ten years!
  Is this something related with the daylight savings time? If so, how do I solve it?
  Is there anything that i am overlooking?</p>
  
  <p><strong>Edit:</strong> Ok, I outputed the time, just to see what happens and this is what I got now:</p>
  
  <pre><code>Date=28-10-2010 Thursday :: 00:00:00
  Date=03-11-2010 Wednesday :: 23:00:00
  Date=10-11-2010 Wednesday :: 23:00:00
  Date=17-11-2010 Wednesday :: 23:00:00
  Date=24-11-2010 Wednesday :: 23:00:00
  </code></pre>
  
  <p>Seems something related with the time, something happens at 2010-11-31...</p>