$table->dateTime('created_at')->default(DB::raw('CURRENT_TIMESTAMP'));
$table->dateTime('updated_at')->nullable();
// if you would set local timezon otherwise skip this
$timezone = "Asia/Dhaka";
date_default_timezone_set($timezone);
// insert created_at value manually
DB::table('table')->insert([
'key'=> 'value',
'created_at' => date("Y-m-d H:i:s", strtotime('now'))
]);