Twig variables are lower cased and underscored.

https://twig.sensiolabs.org/doc/2.x/coding_standards.html

main/exercise/ReadingComprehension.php

@@ -74,7 +74,7 @@ class ReadingComprehension extends UniqueAnswer
         $view->assign('text', nl2br($text));
         $view->assign('words_count', $wordsCount);
         $view->assign('turns', $turns);
-        $view->assign('refreshTime', $this->refreshTime);
+        $view->assign('refresh_time', $this->refreshTime);
         $view->display($template);
     }
 

main/template/default/exercise/reading_comprehension.tpl

@@ -96,6 +96,6 @@
 
         updateView();
 
-        var timeOuId = window.setInterval(updateView, {{ refreshTime }} * 1000);
+        var timeOuId = window.setInterval(updateView, {{ refresh_time }} * 1000);
     });
 </script>