The only part of the app which are affected by users being in a different timezone to the one which is set in the app settings are the App Alerts / Notifications and the On Now icon which appears under “live” agenda sessions.
Any app alerts which are pre-scheduled in the dashboard will be sent out at the time / date they are pre-scheduled for in the selected app time zone. If the time zone is changed after an alert is pre-scheduled, it will still go out at the date / time that it was pre-scheduled to in the time zone when the alert was first created.
The on-now icon / badge which appears under sessions appears when the session is between the start and end date / times within the timezone of the app. It is possible to hide this badge from within one specific agenda within an app, or for all agendas which in an app.