It makes a huge difference that it's a Sunday. On a Sunday I'd allocate 45mins each way for the drive to/from town (can take up to 3hrs on a bad weekday). UberX will cost you around BRL 75 each way.
You could head into town for a lunch/drink (maybe in Pinheiros/Vila Madalena), and maybe walk around Ibirapuera Park and check out the view from the rooftop of the Contemporary Art Museum (MAC-USP) next door. SP is a huge megalopolis and where you go will completely depend on your interests (food, culture, etc)