If your flight is on time I suspect you will be fine

You need to make conformance 35 minutes before departure, which gives you 30 minutes to get from the aircraft to flight connections.

While the boarding pass says the gate closes at 0615 the gate staff will see you are on a connection and I think they can see roughly when you went through conformance. They will do everything they can to get you on the plane! You might be last on, but I think you will make it if your inbound is more or less on time.

I would be more worrying about the A380 overnighting again in JNB