Waiting period for marriage visa application?

So, I'm lying awake nights imagining new possible disasters to torture myself with.

I plan to marry my UK fiance in January here in the US and then apply for a marriage visa immediately, if not sooner. It just occurred to me that there might be such a thing as a waiting period after the marriage takes place before I can apply. Does anyone know if there's any reason I can't apply within a day or two of the marriage, as long as I have all of my documents prepared?

A sort of related question is, assuming that my visa is granted, is it effective immediately? In other words, can I book my flight the moment I hear the happy news?

Thanks so much. Maybe I'll be able to sleep tonight. 

You can apply immediately after you are married.

The visa will be made valid from the date you put on the application.  You will have 30 days to enter the UK from the date the visa is issued.

Thank you, KF. You've set my mind at ease. That's exactly what I needed to know.