fix cache keys timeout.

examcloud-core-oe-admin-service/src/main/java/cn/com/qmth/examcloud/core/oe/admin/service/cache/ExamStudentCache.java

@@ -44,8 +44,7 @@ public class ExamStudentCache extends RandomObjectRedisCache<ExamStudentCacheBea
 
     @Override
     protected int getTimeout() {
-        // 1天
-        return 60 * 60 * 24;
+        return 60 * 60 * 12;
     }
 
 }