I did a simple speedtest this morning and what a beautiful graph, I will monitor today and see what happens
http://www.speedtest.net/my-result/3382826221
One can see from my router graph that the speed picked up at midnight approached.
http://hostmypicture.com/images/internqjq.png
View attachment 106642
What does this tell you?
When I did my first test yesterday it was showing everything was A-ok, but that was still relatively early in the traditional peak time period. Later when I did the test again mine also dropped, which in my humble opinion means that the network are under strain due to demand. I would think this is more an Afrihost constraint, but this does not mean however that a local exchange are congested as well.
The reason why I think it's Afrihost is because when other ISPs accounts are being used that the problem disappears for some.
I downloaded "Die Burger" this morning before I left for work and the speed was back to standard full speed.
In your case it also appears that you have better performance is the non peak periods. I also think you need to test with another ISP account at the times you have throughput issues to determine if it's an exchange issue or an Afrihost issue. If you are really unlucky then you have both an Afrihost and exchange problem in the peak times.