The temperature tends to fall reasonably quickly as the sun sets and the cool ocean air moves in over the beach, and it's the strangest feeling to leave the beach and the refreshing 19°C air and walk up the many steps to the parking areas to be met with the preceding day's oven-hot air.
If you are visiting Cape Town at this time of the year - pack a picnic dinner, add a few candles, grab a sweater, and head on down to Clifton 4th beach at about 18h30. Feel free to thank me later. ;)