My advice would be to forget driving unless you are on a motorbike. You need to allow at least 90 minutes to get to Hounslow via the south circular, which vile though it is, is the most direct route. Much better to get the Victoria service from the station to Clapham Junction and then go to Hounslow from there. If you link it up optimally it is well under an hour station-to-station. Good luck!