<?php
// CRUD for domain-level settings
civicrm_api('DomainSetting','create', array(
  'domain_id' => $ // optional; default current domain
  'timezone' => $,
));
// CRUD for contact-level settings
civicrm_api('ContactSetting','create', array(
  'contact_id' => $ // optional; default current user
  'timezone' => $,
));
// R for settings
civicrm_api('Setting', 'get', array(
  return => 'timezone',
));