I agree with Karen2 about The Tech museum --you'll only be one block from there. Call now to get tickets, or call the St. Claire and ask the concierge to get them for you, to see both Everest and The Living Sea at the IMAX theater. If you've never been to an IMAX, it's absolutely amazing. You'll forget everything else and be absorbed by the experience. Tickets in the evenings do sell out in advance. Beginning at 7:00 p.m., there is a double feature of Everest, followed by The Living Sea. Tickets for the double feature are $14 for adults, $11 for children. This does not include admission to The Tech Museum, which is an additional $8, but is worth it. Lots of fun displays in there. The phone number, if you want to order tickets and find out more info, is 408/279-7150.
That could take up your Friday evening.
As for Saturday morning, if you only have 5 hours, I would stick around the South Bay. You don't want to risk a traffic jam somewhere and be late or even miss the wedding. You can save San Francisco for another time, when you can give it the time it deserves.
Enjoy!