Announcements are rich messages that go out to every single one of your guests. You can schedule them for any timezone you'd like by selecting the applicable timezone in the drop down when building the Announcement in the Platform.
The "Launch Time" and "Take Down Time" will determine how long the universal rich message displays in the app for all guests.
If further assistance is required, submit a ticket to Punchh Support. (For help submitting a ticket, click here)