Here my outcome looks like this, please have a look
array(4) 
{ 
    [0]=> string(5) "12:00" 
    [1]=> string(5) "12:20" 
    [2]=> string(5) "12:40" 
    [3]=> string(5) "01:00" 
} 
array(2) 
{ 
    [0]=> string(5) "02:00" 
    [1]=> string(5) "02:20" 
}
Here is my code
   $t_i=$this->Hospital_model
             ->get_time_interval_break_split(
                     $t_i_b->start,
                     $t_i_b->end,
                     $consult_time);
$output =array_merge($t_i);
Here is my model
public function get_time_interval_break_split($start_time,$end_time,$consult_time)
{
   $array = array();
   $time_diff = $consult_time * 60;
   if(!empty($start_time))
   {
      for ($i=strtotime($start_time); $i<=strtotime($end_time); $i += $time_diff)
      {  
         $array[] = date("h:i", $i);
      } 
   }
   return $array;
 }
now i want to combine those two arrays in to one and i had used array_map,array_merge and all but didn't got a solution,please help me to solve