Channa beat me to it. However long you wish to stay in SFO, you do eventually want to reach EWR, right? I'd be proactive and call just before the original flight, say you're having trouble making the connection. One could be stuck in SFO for so many reasons, they won't ask. Worst case they tell you your last leg is dead, and that's on them, not you. Best case, you visit SFO and still complete your trip.