The spell is cast and Sansa really won't feel herself moving faster at first. However, if she takes note of the world around her, it will have seemed to slow. The branches swaying in the wind are doing so more slowly, the leaves rustling slower too. Even the sound of the dragon's beating wings are now slower. In truth, the pair are moving faster now, it just doesn't present itself as running fast. Christine leads them into the thicket, hoping for heavy cover or maybe an outcropping of rock. The Hinterlands is full of such formations.