diff --git a/classes/cachemanager.php b/classes/cachemanager.php
index dbb4972..1336375 100644
--- a/classes/cachemanager.php
+++ b/classes/cachemanager.php
@@ -16,6 +16,8 @@
 
 namespace mod_learningmap;
 
+use core\clock;
+
 /**
  * Cache manager class for mod_learningmap
  *
@@ -104,7 +106,8 @@ public static function build_backlink_cache(int $courseid = 0) {
 
         if (empty($courseid)) {
             // Finally set the flag to indicate that the cache is properly built.
-            $cache->set('fillstate', time());
+            $clock = \core\di::get(clock::class);
+            $cache->set('fillstate', $clock->time());
         }
     }
 
diff --git a/classes/task/fill_backlink_cache.php b/classes/task/fill_backlink_cache.php
index 3274bbb..bcf3307 100644
--- a/classes/task/fill_backlink_cache.php
+++ b/classes/task/fill_backlink_cache.php
@@ -16,6 +16,7 @@
 
 namespace mod_learningmap\task;
 
+use core\clock;
 use mod_learningmap\cachemanager;
 
 /**
@@ -48,8 +49,9 @@ public function execute() {
 
         $fillstate = $cache->get('fillstate');
 
+        $clock = \core\di::get(clock::class);
         // If the cache is filled within the last 24 hours, do nothing.
-        if (!empty($fillstate) && $fillstate > time() - 60 * 60 * 24) {
+        if (!empty($fillstate) && $fillstate > $clock->time() - 60 * 60 * 24) {
             mtrace('Backlink cache is already filled within the last 24 hours. Exiting.');
             return;
         }
diff --git a/tests/mod_learningmap_backlink_cache_test.php b/tests/mod_learningmap_backlink_cache_test.php
index 07f2576..a2353e4 100644
--- a/tests/mod_learningmap_backlink_cache_test.php
+++ b/tests/mod_learningmap_backlink_cache_test.php
@@ -16,6 +16,8 @@
 
 namespace mod_learningmap;
 
+use core\clock;
+use mod_learningmap\task\fill_backlink_cache;
 use stdClass;
 
 /**
@@ -225,4 +227,40 @@ public function test_backlink_generation(): void {
         $descriptionafter = $PAGE->activityheader->export_for_template($OUTPUT)['description'];
         $this->assertEquals($descriptionbefore, $descriptionafter);
     }
+
+    /**
+     * Tests if the nightly task only runs the whole rebuild every 24h.
+     *
+     * @covers \mod_learningmap\task\fill_backlink_cache
+     */
+    public function test_backlink_cache_rebuild_task(): void {
+        $this->resetAfterTest();
+        $cache = \cache::make('mod_learningmap', 'backlinks');
+        // Set clock to current time.
+        $clock = $this->mock_clock_with_frozen(time());
+        $task = new fill_backlink_cache();
+        ob_start();
+        $task->execute();
+        $output = ob_get_contents();
+        ob_end_clean();
+        $this->assertStringContainsString('Building backlink cache started', $output);
+
+        // We now have built the backlink cache.
+        // We reset the clock to a time which is less than 24h hours in the future.
+        $clock->set_to($clock->time() + 23 * 60 * 60);
+
+        ob_start();
+        $task->execute();
+        $output = ob_get_contents();
+        ob_end_clean();
+        $this->assertStringContainsString('Backlink cache is already filled within the last 24 hours', $output);
+
+        // We reset the clock to a time which is more than 24h hours in the future.
+        $clock->set_to($clock->time() + 25 * 60 * 60);
+        ob_start();
+        $task->execute();
+        $output = ob_get_contents();
+        ob_end_clean();
+        $this->assertStringContainsString('Building backlink cache started', $output);
+    }
 }