It's very important to start the process early on because the process is lengthy and may take a few months so if your visa expires before your application papers go through, you'll be required to leave the country and start the process from the beginning.
Kubaluleke kakhulu ukuqala inqubo ngaphambi kwesikhathi ngoba inqubo yinde futhi ingathatha izinyanga ezimbalwa ngakho-ke uma i-visa yakho iphelelwa yisikhathi ngaphambi kokuba amaphepha akho okufaka isicelo adlule, uzodingeka ukuthi uphume ezweni bese uqala inqubo kusukela ekuqaleni.