I read that the max time to be in transit without a visa and remain airside, for a connection was 7 hours, but also read it's irregularly enforced. The airline you board to get to GRU will be the first to decide if you can enter. I'd check this out. If you can indeed enter, then I'd "splurge" on a one-day pass at an airline club, or go to the small transit "hotel." I seem to recall also seeing a spa where you could kill time. Very limited dining options airside. No pools airside, but some clubs have showers (I think United, for one, does).