Problem wich HTML 5 search on 3.2.5

Hello again.
I have to add that i am free.fr user and free use php 5.1 which do not have DateTime class.
What i dont understand is that this class was used in previous versions of customizr without visible error.
I found this code to emulate this class :
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[ Moderator note: code fixed. Please wrap code in the backtick character or use the code button. ]

if (!class_exists('DateTime')) {
class DateTime {
public $date;

public function __construct($date) {
$this->date = strtotime($date);
}

public function setTimeZone($timezone) {
return;
}

private function __getDate() {
return date(DATE_ATOM, $this->date);
}

public function modify($multiplier) {
$this->date = strtotime($this->__getDate() . ' ' . $multiplier);
}

public function format($format) {
return date($format, $this->date);
}
}
}

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But where should i put it ? In customizr-child/functions.php ?
Thanks