Thamathu Pass is probably your best option, since its very direct, has a good path and is very easy. Havent tried up and and down in a day, so not totally sure if it can be done in 6-7 hours, but at a good pace it probably can be. You could at least make it to Thamathu Cave and decide if you want to carry on. If you make it to the top with good time to spare, then consider descending Ngwangwane Pass(Bushman's Pass). This is a very easy pass, but a little longer walk than Thamathu.