UX: Display error message if no time frame selected in topic status update

app/assets/javascripts/discourse/controllers/edit-topic-timer.js.es6

@@ -103,6 +103,14 @@ export default Ember.Controller.extend(ModalFunctionality, {
 
   actions: {
     saveTimer() {
+      if (!this.get("topicTimer.updateTime")) {
+        this.flash(
+          I18n.t("topic.topic_status_update.time_frame_required"),
+          "alert-error"
+        );
+        return;
+      }
+
       this._setTimer(
         this.get("topicTimer.updateTime"),
         this.get("topicTimer.status_type")

config/locales/client.en.yml

@@ -1809,6 +1809,7 @@ en:
         when: "When:"
         public_timer_types: Topic Timers
         private_timer_types: User Topic Timers
+        time_frame_required: Please select a time frame
       auto_update_input:
         none: "Select a timeframe"
         later_today: "Later today"