Add a warning message to products that are out of timeframe

src/pretix/control/templates/pretixcontrol/item/base.html

@@ -36,6 +36,12 @@
                 item to an existing or newly created quota.
             {% endblocktrans %}
         </div>
+    {% elif not object.is_available_by_time %}
+        <div class="alert alert-warning">
+            {% blocktrans trimmed %}
+                This product is currently not being sold since you configured below that it should only be available in a certain timeframe.
+            {% endblocktrans %}
+        </div>
     {% endif %}
     {% block inside %}
     {% endblock %}