Why are your options only 1h30 and 5hrs? there are multiple flights every hour DUR-JNB/DUR-HLA.
I don't know the timing of the new BA flight, but unless it's scheduled as such that you have a chance of getting stuck behind the TK or EK flight, I would think 1h30 is more than plenty, as long as it is sold on the same ticket of course, I'm also assuming you have to collect your luggage and re-check