Sort events by time

app/models/event.rb

@@ -288,6 +288,10 @@ class Event < ApplicationRecord
     program.conference
   end
 
+  def <=>(other)
+    time <=> other.time
+  end
+
   private
 
   ##

app/models/program.rb

@@ -20,7 +20,7 @@ class Program < ApplicationRecord
     end
 
     def with_registration_open
-      select { |e| e if e.registration_possible? }
+      select { |e| e if e.registration_possible? }.sort
     end
 
     # All confirmed events of the conference with attribute require_registration