diff --git a/tutorial/4-time_window.arl b/tutorial/4-time_window.arl
index 171c8e7..e6f2699 100644
--- a/tutorial/4-time_window.arl
+++ b/tutorial/4-time_window.arl
@@ -1,6 +1,6 @@
-archetype time_window
+archetype time_window(const creation_date : date)
 
-variable creation : date = now
+variable creation : date = creation_date
 
 entry payback_after_period () {
   ///////////////////////////////////////////////////////////////////