Setting a timezone will change the time of your event.
By default, automatic timezone is based on your location. Setting a custom timezone can be helpful if you're hosting an event that is located somewhere in a different timezone than where you are right now.
Custom Timezone for all Events
This will set a custom timezone for all your current and future events
This settings is found under User Settings at the top right > Default Event Settings
Custom Timezone for a specific Event
This will set a custom timezone just the selected event
This settings is found when managing the selected event -> Settings Page -> Event Timezone