You can redeem miles for any seat available for sale at any time but it requires A LOT of miles as it’s linked to the price of the ticket. Otherwise SAA makes space available periodically when they run JourneyBlitz/SaverBlitz promos at the better miles redemption rates. The timing of these promos is a bit haphazard but there are usually three or four a year and always one in February or March before miles expire.

Platinum members (and I believe Nedbank Voyager credit card and Discovery members) get early access (whether all at once or staggered/platinums first and then bank cards holders I don’t know…).

As for JNB/CPT-GRU, J awards through JourneyBlitz and SaverBlitz promos are hard to come by (read never) but Y is plentiful. Be aware of the high surcharges however meaning that you’re probably only saving R2-3k one way when compared to a paid ticket. Similar on domestic redemptions where the surcharge is around R900 on a one way vs a paid ticket in the region of R1400.

A much better use of voyager miles is for cabin upgrades (but you need to buy a flexible fare class). Awards are easier to secure on JNB-GRU on certain days of the week and more difficult for Cape Town (especially on the weekend flights!). Always call Voyager to confirm there is E class availability (the award upgrade class) on your preferred flight BEFORE you buy the ticket. My experience is that once E class is gone SAA won’t make more available, and only very rarely on the day of the flight if you are a status holder and there are unsold seats. If there is no E class availability for your preferred flight then don’t buy the flexible upgradable fare class (my view).

More generally Voyager is quite restrictive when it comes to awards - especially on star alliance carriers where you can only redeem a return and not one way rewards. Unless you plan on flying SAA a lot and using the miles for cabin upgrades or the occasional Y redemption when there are JourneyBlitz promotions I would think carefully.