Question : How long do most people stay in Stuttgart when they fly in from Johannesburg?
Answer : Of course you're not most people, but if you were, you'd stay roughly 20 days.
Question : Is price more important than specific travel days for you?
Answer : Monday is your cheapest day to fly in December. Having flexibility in your travel plans means you can save, so be sure to plan ahead when possible.
Question : Are prices changing frequently for this route?
Answer : Flight prices for JNB to STR change a lot more than most. The further out you book a route, the more likely you are to save.