90 days is today but the web site is not taking it yet - hence my question. It may well be that the 90 days is local for departure (JNB at 1800 local).
On-line it's to the hour, or to put it another way, it opens up exactly 2160 hours before the actual scheduled (local) departure time of your flight.
As I mentioned you can also telephone any time on the day and request - the QFF agents are not so constrained.