By default the web dashboard will use your browser's local timezone for scheduling. You can change this under Account > Office Preferences > Localization. Once changed, you'll see times update to reflect the new time zone throughout the web dashboard. Give the page a refresh after updating for the best results.
You can confirm the active timezone in the bottom right of your screen.
This feature is used by the web dashboard only for now. Other apps (e.g. mobile) will rely on your device settings.