If you wish to visit Cape Town, the months of April/May I have always been told, they get winter rains June/July/August. It is a beautiful province with a lot to see and do.
East Coast up in KwaZulu-Natal, I would suggest May/June as being the better time, to avoid the extremely hot summer months of December/January. We have summer rains from September to February.
Our school children also take Christmas holidays December/January and everywhere along the coastline (even thought it is a long coastline) fills up with holiday makers.
Our country is big, travel from Cape Town to Durban will take a couple of days, each province has different beauty to offer, each region will have nature reserves.
Thank you @joanstewart for the detailed info. I would most likely prefer December-January, because it is not easy to survive the snowy, long nights and short days , winter days. We need some sun at that time:)
Longer days in Cape during that time of the year, buy sunscreen lotion and enjoy planning there is much to do no matter where you decide to tour.