// For Drupal 7, uncomment this line to set a new cache lifetime:
// $conf['page_cache_maximum_age'] = 21600;
// For the current Drupal version, uncomment this line to set a new cache lifetime:
// $config['system.performance']['cache']['page']['max_age'] = 21600;

// Verify we're on an Acquia-hosted environment.
if (file_exists('/var/www/site-php')) {
  if (isset($_ENV['AH_SITE_ENVIRONMENT'])) {

    // Alter '01dev,' '01test', and '01live' to match
    // your website's environment names.
    // Alter the variable names to match your version of Drupal:
    //   The current Drupal version uses $config['system.performance']['cache']['page']['max_age']
    //   Drupal 7 uses $conf['page_cache_maximum_age']

    switch ($_ENV['AH_SITE_ENVIRONMENT']) {
      case '01dev':
        // Cache settings.
        $config['page_cache_maximum_age'] = 0;
        break;
        case '01test':
        // Cache settings.
        $config['page_cache_maximum_age'] = 3600;
        break;
        case '01live':
        // Cache settings.
        $config['page_cache_maximum_age'] = 21600;
        break;
    }
  }
}

<?php
/**
* @file
*
* This post-settings-php hook is created to conditionally set the cache
* lifetime of Drupal to be a value that is greater than 300 (5 minutes).
* It also does not let you set it to be lower than 5 minutes.
*
* This does not fire on Drush requests, as it interferes with site
* creation. It also means that drush will report back incorrect values for
* the cache lifetime, so using a real browser is the easiest way to
* validate what the current settings are.
*
* How to enable this for a site:
*  - drush vset acsf_allow_override_page_cache 1
*  - drush vset page_cache_maximum_age 3600
*/
if (!drupal_is_cli()) {
  $result = db_query("SELECT value FROM {variable} WHERE name = 'acsf_allow_override_page_cache';")->fetchField();
  if ($result) {
    $acsf_allow_override_page_cache = unserialize($result);
    if ($acsf_allow_override_page_cache) {
      $result = db_query("SELECT value FROM {variable} WHERE name = 'page_cache_maximum_age';")->fetchField();
      // An empty array indicates no value was set in the database, so we ignore
      // the site.
      if ($result) {
        $page_cache_maximum_age = (int) unserialize($result);
        if ($page_cache_maximum_age > 300) {
          $conf['page_cache_maximum_age'] = $page_cache_maximum_age;
        }
      }
    }
  }
}