This will be a short diary.
I'm not giving formal legal advice here, but I can tell you that assuming Judge Walker's stay is lifted, there may be a very short span of time until a higher court issues a stay. It could be the Ninth Circuit. It could be Circuit Justice Anthony Kennedy, or it could be the Supreme Court.
Walker could delay the effect of his order for a certain amount of time to give them a chance, or not. We just don't know. But if you want to get married, consider going to get in line now. The ruling might come today. It might not. I know some places require an appointment, some don't. But, you may only have a few hours. I wouldn't want anyone who wants to get married to be the last person in line. The thought breaks my heart.
Yes, you may have to wait, and you may have to wait for nothing. But this may be a small window. This is just my two cents and something I've told some friends. Please be aware it could be a fruitless wait, but it might be the difference.
UPDATE: Yes, this is only in California. And no, there's probably no need to stay overnight now that they're probably all closed. I mean, it's not like an iPad or something. (=
Depending on what happens with the stay, if you're a lawyer, consider going down to the clerk's office and seeing if people need help. I am planning on it in my county.