SEA-SFO connection at 68 min. is pushing minimums IMO (done this dozen's of times). If you really want to make the fight, increase the connection time to 2 hr minimum in sfo, all it takes is low-clouds at either airport and your day is ruined. There is more chance than not of this occurring. the only way to avoid this on day of travel is the hope of SDC to an earlier delayed flight (Which of course requires availability). YMMV. Good luck.