--- C:/temp/_PATCHES/safe_cache_form_clear/a/safe_cache_form_clear.module	Mon Feb 22 20:58:00 2016
+++ C:/temp/_PATCHES/safe_cache_form_clear/b/safe_cache_form_clear.module	Mon Feb 12 17:15:59 2018
@@ -26,7 +26,7 @@
   $results = db_select('cache_form')
     ->fields('cache_form', array('cid'))
     ->condition('expire', CACHE_PERMANENT, '<>')
-    ->condition('expire', REQUEST_TIME, '<')
+    ->condition('expire', REQUEST_TIME+19800, '<')  // fake $expire to 30 min instead of default 6 hours (=(6-0.5)*3600)
     ->range(0, $limit)
     ->execute();