There are three different ways to assign time zones.
You assign an account time zone in your Account Settings (cog icon) → Company Details. This sets the default time zone for all staff.
2. You can assign a time zone to a Location in the Company → Locations page.
3. Each user can assign their own personal time zone (should it differ from the account default) by clicking the Cog icon →Your Details.
Once this is set up, you'll see a globe icon above the rota indicating the time zone.
Please note: Location time zones and account-wide time zones only apply to the Rotas page. Everything else, including the Dashboard, run off the personal time zone of the logged in user.