Definitely no hitchhiking. If you must visit downtown shopping areas, the safest time is in the morning when muggers tend to be asleep. From midday onwards the activity of robber gangs increases considerably as members become drunk, drugged and short on money. After dark you're a goner. Don't become their walking goldmine.
Muggers invariably carry knives and often guns.
Generally stay indoors after dark and enjoy the hospitality of your backpacker bar etc. Make your own decisions. Don't get drawn into dicey situations by unthinking companions. Follow these road rules and you will find South Africa a wonderful country to visit. Choose one and phone them to get picked up.