maybe now

app/controllers/assignments_controller.rb

+require 'icalendar/tzinfo'
+
 class AssignmentsController < ApplicationController
   before_action :set_session, :set_users
 
@@ -63,6 +65,8 @@ class AssignmentsController < ApplicationController
 
       format.ics do
         calendar = Icalendar::Calendar.new
+        tz = TZInfo::Timezone.get('UTC')
+        calendar.add_timezone tz.ical_timezone Time.now
 
         @user.assignments.each do |assignment|
           session = assignment.session