A lot of things in Jomablue display times (such as Sessions) or are triggered at certain times (Email and SMS Campaigns), all of which require the Timezone to be set under Event Settings.
All dates and times displayed for an event in Jomablue is displayed in the Event Time Zone (not your timezone).
So if you live in San Francisco but schedule a campaign for a event in Singapore, select the SMS campaign to send at 9am inside of Jomablue. It will be sent at 9am Singapore time.
The Timezone for each event is set in Event Settings.
Jomablue automatically handles timezone conversions and transitions between daylight savings times. Although you should be careful to avoid scheduling campaigns and then changing the Event Timezone (although a rare scenario).
Scheduling Campaigns then changing the Event Timezone
When scheduling a campaign, the original timezone is stored within the campaign parameters. Therefore if you change the timezone after a campaign has been set, the campaign won't be updated to reflect the new timezone. You would have to rescheduled the campaign with the new (and correct) timezone in Event Settings.