Grand taxis, buses, and minibuses to the Ourika Valley leave from Bab er Robb in Marrakesh, starting from around 6am. They run until mid-morning and return in the late afternoon or evening — enough time to make it a comfortable day trip. The journey to Setti Fatma takes about two hours.
You can also rent a car or a 4x4 in Marrakesh. A rental vehicle gives you flexibility to stop along the valley and is worth considering in spring, when the road can deteriorate beyond the reach of ordinary cars.