Miami is 6 hours behind Johannesburg
Best overlap: 2:00 PM to 6:00 PM in Johannesburg is 8:00 AM to 12:00 PM in Miami.
Keep meetings inside 2:00 PM to 6:00 PM in Johannesburg — that maps to 8:00 AM to 12:00 PM in Miami. Around 4 hours of overlap is enough to work comfortably, as long as meetings don't drift to the end of one team's day. These times hold for most of the year, but Miami's daylight saving (which Johannesburg doesn't use) shifts them by an hour twice annually.