There are 3 different ways to assign time zones.
1. You assign a client time zone in your account settings (cog icon), which sets the default time zone for all staff.
2. You can assign a time zone to a location on the Locations page (via Company), by clicking a location to edit it.
3. Each user can assign their own personal time zone (should it differ from the client default), in the "Your Details" tab of your account settings.
Once this is set up you will see above the rota there is a globe icon and time zone city. By default it displays what the location time zone is set to. However, if you click it you can change the time zone to either your user default or a custom time zone of your choice. The system remembers the selection you make here, so when you switch between locations it will always display in whatever you last picked.
Please note, location time zones and custom time zones only apply to the Rotas page, the dashboard and everything else run off your user time zone.