Remove the time limit imposed by Drupal 7's node_access_rebuild function by hacking core.

unlimited_node_access_rebuild_time.patch

diff --git a/modules/node/node.module b/modules/node/node.module
index dbb1a65..a750cf9 100644
--- a/modules/node/node.module
+++ b/modules/node/node.module
@@ -3634,7 +3634,7 @@ function node_access_rebuild($batch_mode = FALSE) {
     }
     else {
       // Try to allocate enough time to rebuild node grants
-      drupal_set_time_limit(240);
+      drupal_set_time_limit(0);

       // Rebuild newest nodes first so that recent content becomes available quickly.
       $nids = db_query("SELECT nid FROM {node} ORDER BY nid DESC")->fetchCol();