It is important to know that there are certain periods of the year less interesting than others.

Approx one month visit.

The best periods for a visit are as follows:
Netherlands to South Africa: during the April, May, June, August, September periods
South Africa to the Netherlands: during March, April, May, November, December periods.

One year visit.

The best periods for a visit are as follows
Netherlands to South Africa starting January at the beginning of the academic year.
South Africa to the Netherlands starting September at the beginning of the academic year.