$a = array(
  array("item"=>"apple", "start"=>"24-03-2018 01:00:00"),
  array(item"=>"orange", "start"=>"24-03-2018 04:00:00"),
  array(item"=>"pineapple", "start"=>"24-03-2018 03:00:00")
);

$currentTime =  new DateTime(date('Y-m-d H:i:s'));

foreach ($a as $b) {
 $currentTime = $currentTime->modify('+01 seconds');
    if ($currentTime >= $b['start]) {
    //start countdown and increase by every second
    }
   var_dump($b);
}