Doing Durban in two nights? Completely possible. And in my opinion, quite enough.
My day in Durban (all on foot):
am – Walked into/through town and market street. Looked at the strange produce at Victoria Market, including but certainly not limited to goats heads, ONLY R40 each.
noon – bought a bunny chow (half a hollowed loaf of bread filled with curry – neither the easiest nor prettiest thing to eat but damn good) and ate it in the park near the anti AIDS monument. Along with a side of people watching and napping.
pm – walked along the beach and went “swimming” in the sea. Very importantly bought an ice cream. Had a rooftop braai and a couple of savannahs with new friends at Happy Hippo backpackers.
Hostel/transport: If you want to be close to the beach and Usharka, Happy Hippo Backpackers is an ideal place. Huge building with a large self cater kitchen, rooftop bar and braai facilities. The bedrooms and bathrooms are good with plenty, actually bucket loads, of communal space. If you would like to be close to the town centre, clubs and stadium you are better off staying somewhere else. It is possible to walk everywhere though it is a large distance to cover. Uber is popular in the city so if you want to get as much sight seeing into your day it is a reasonable choice.