Returning bunch of matrices using RCPP in C++ in an efficient way using a list

I am trying to return a bunch of matrices using RCPP. My code below is extremely inefficient. I would like to know if the following code can be efficient.

#include <RcppArmadillo.h>
// [[Rcpp::depends(RcppArmadillo)]]

// [[Rcpp::export]]
Rcpp::List hello( 
    const arma::rowvec& g,
    const int& n, 
    const int& p,
    const arma::mat& S,
    const arma::mat& zc,
    const arma::rowvec& dl){
  Rcpp::List ht(n);

  for(int t=0; t < n;++t){

    arma::mat hhat(p,n);
    hhat.fill(0.0);
    for(int i = 0;i < n; ++i){
      arma::mat h(p,1);
      h.fill(0.0);
      if (t > i){
        for(int u=i;u <= t; ++u){
          arma::rowvec zr = zc.rows(i,i);
          h += exp(arma::as_scalar(g*zr.t())) * (zr.t() - S.cols(u,u))*dl(u);
        }
      }
      hhat.cols(i,i) = h;
    }
    ht[t] = hhat;
  }

  // Specify list length
  Rcpp::List res(1);
  res[0] = ht;

  return(res);
}

Here is the example.

g=c(1,2.1,3.1)
n=1600
p=3
S = matrix(rnorm(4800),nrow=3,ncol=1600)
dl=runif(1600)
z=matrix(runif(4800),nrow=1600,ncol=3)
ptm=proc.time();kkk= hello(g=g,n=n,p=p,S = S,zc=z,dl = dl);proc.time()-ptm;
 user  system elapsed 
  31.25    0.00   31.30 

Any help would be appreciated.

Following the updated code. Initially I was returning list of a list. Now it returns a list. This reduces the computing time by 10 seconds. I hope this code can be improved further.

#include <RcppArmadillo.h>
// [[Rcpp::depends(RcppArmadillo)]]

// [[Rcpp::export]]
Rcpp::List hello( 
    const arma::rowvec& g,
    const int& n, 
    const int& p,
    const arma::mat& S,
    const arma::mat& zc,
    const arma::rowvec& dl){
  Rcpp::List ht(n);


  for(int t=0; t < n;++t){

    arma::mat hhat(p,n);
    hhat.zeros();
    for(int i = 0;i < n; ++i){
      arma::mat h(p,1);
      // h.fill(0.0);
      h.zeros();
      if (t > i){
        for(int u=i;u <= t; ++u){
          //arma::rowvec zr = zc.rows(i,i);
          h += exp(arma::as_scalar(g*zc.row(i).t())) * (zc.row(i).t() - S.col(u))*dl(u);
        }
      }
      hhat.col(i) = h;
    }
    ht[t] = hhat;
  }

  // Specify list length
  // Rcpp::List res(1);
  // res[0] = ht;

  return(ht);
}