I'd recommend at least 1+ hours spent there; as a Disney fan you'd definitely enjoy taking your time and looking at the galleries in detail. My recommendation is budget your time to not wear yourself out; a lot of people focus intensively on the first couple rooms (about Walt's early life) and then poop out by the 1930s/40s with the feature films.
This is probably too late to help the original poster, but maybe it can be of use to others.
Plan to spend more time than you think you'll need. I have gone twice, and spent 4 hours each time, and still haven't seen it all. Both times I went to the museum we had a limited amount of time to spend there, hence the two 4-hour trips.
If you are a Disney nerd, you could easily spend all day there.
More casual Disney fans will still easily be able to fill up several hours.
proud member of Rally team It Doesn't Matterhorn, winners of the 2012 Team Spirit award
Driving thru SF on a weekend is not something I
am looking forward to.
Hope the museum is worth the drive.
It's definitely worth the drive through San Francisco.
It's even worth a drive from LA up to San Francisco!
Like Bookwyrm says plan for more time than you think you will need.
Minimum 3 hours, but you could take all day if you like.
Disney Magic puts a lot more into the building than you may think possible.