Caching sessions with pam_timestamp on ubuntu

I am trying to use PAM and the pam_timestamp module to reduce the number of passwords I need to enter.

Test program via https://learning.oreilly.com/library/view/linux-security-cookbook/0596003919/ch04s01.html#linuxsckbk-CHP-4-SECT-1.2:

#include <security/pam_appl.h>
#include <security/pam_misc.h>
#include <pwd.h>
#include <sys/types.h>
#include <stdio.h>
#define MY_CONFIG "myconfig"
static struct pam_conv conv = { misc_conv, NULL };

main( )
{
  pam_handle_t *pamh;
  int result;
  struct passwd *pw;
  if ((pw = getpwuid(getuid( ))) == NULL)
    perror("getpwuid");
  else if ((result = pam_start(MY_CONFIG, pw->pw_name, &conv, &pamh)) != PAM_SUCCESS)
    fprintf(stderr, "start failed: %d\n", result);
  else if ((result = pam_authenticate(pamh, 0)) != PAM_SUCCESS)
    fprintf(stderr, "authenticate failed: %d\n", result);
  else if ((result = pam_acct_mgmt(pamh, 0)) != PAM_SUCCESS)
    fprintf(stderr, "acct_mgmt failed: %d\n", result);
  else if ((result = pam_end(pamh, result)) != PAM_SUCCESS)
    fprintf(stderr, "end failed: %d\n", result);
  else
    fprintf(stderr, "SUCCESS!\n");
}

Test pam config, /etc/pam.d/myconfig - this is straight out of the man page

           auth sufficient pam_timestamp.so verbose
           auth required   pam_unix.so

           session required pam_unix.so
           session optional pam_timestamp.so

However, when I run the test program, it always asks for the password, i would have expected it to not ask after the timestamp file is created.

nfultz@neal-slg2:/tmp/pamapp$ ./a.out 
Password: 
SUCCESS!
nfultz@neal-slg2:/tmp/pamapp$ ./a.out 
Password: 
authenticate failed: 7

This is on Ubuntu 23.04 if that matters.