Intrigued by this post, I went searching for the SA AIP (http://www.caa.co.za/Pages/Aeronauti...blication.aspx) to check what is called "day" in the local AIP. Although I found about 190 occurences of the words "day" or "daytime" in the GEN and ENR parts, I was unable to find a valid definition of these terms.

The SA AIP gives SR and SS tables for different Airports, but not for Douglas.

In my country, "day" is clearly defined in the AIP as SR-30' SS+30'; I know of other countries where it is between civil twilights. Where did you get the SR-15' SR+15' from?