Awesome PHP Date Increment

I was trying to do a loop to find the weekend between two dates and something was really weird weird.

I need to follow some code, which I think should work fine.

$weekends = array();
// yyyy-mm-dd
$firstWeekend = '2015-09-04';
$lastWeekend = '2015-12-25';
$firstWeekendTime = strtotime($firstWeekend);
$lastWeekendTime = strtotime($lastWeekend);

$totalWeekends = 0;
for ($i = $firstWeekendTime; $i <= $lastWeekendTime; $i += (7 * 86400)) {
  $totalWeekends++;
  $weekends[date('Y-m-d', $i)] = array(
    date('Y-m-d', $i),
    date('Y-m-d', strtotime(date('Y-m-d', $i) . '+ 2 days'))
  );
}

      

        
        
        
      

    

Eg. Output:

[2015-10-16] => Array
    (
        [0] => 2015-10-16
        [1] => 2015-10-18
    )

[2015-10-23] => Array
    (
        [0] => 2015-10-23
        [1] => 2015-10-25
    )

[2015-10-29] => Array
    (
        [0] => 2015-10-29
        [1] => 2015-10-31
    )

[2015-11-05] => Array
    (
        [0] => 2015-11-05
        [1] => 2015-11-07
    )

      

        
        
        
      

    

But this is not true, because the next weekend after 2015-10-23 is 2015-10-30. So the output should be as follows:

[2015-10-16] => Array
    (
        [0] => 2015-10-16
        [1] => 2015-10-18
    )

[2015-10-23] => Array
    (
        [0] => 2015-10-23
        [1] => 2015-10-25
    )

[2015-10-30] => Array
    (
        [0] => 2015-10-30
        [1] => 2015-11-01
    )

[2015-11-05] => Array
    (
        [0] => 2015-11-05
        [1] => 2015-11-07
    )

      

        
        
        
      

    

I finally did it by setting the default timezone and not striking out anything else, it worked.

date_default_timezone_set('America/Los_Angeles');

      

        
        
        
      

    

Can anyone understand why this increment is failing without a timezone? And the strangest thing is that it only fails around ~ 2015-10-25

I don't want other options to find the weekend ... I just want to understand why it acts like that.

Thank.