As Ryuk explains, Light can burn the page with Watari's name on it within the 48 hours to cancel his impending death; however, this method can only be used to save a victim of the Death Note once.
As Ryuk explains, Light can burn the page with Watari's name on it in order to cancel his impending death, so Light gives Watari 48 hours. However, this method can only be used to save a victim of the Death Note once.