When is white balance set?

Since "Auto" does the same thing as "Custom" when the center circle is over a neutral color, it may be easier to use AUTO, aim at something neutral and lock WB, rather than go through the Custom thing in places where light varies a lot or time is short.
Is WB set when exposure is set, when focus is set, or when the picture is taken? I'd guess at exposure lock time, but don't know....need to set up the lock functions to allow setting the right combination of stuff together..

As I just learned, WB is set post-exposure, from the data within the center metering circle. So CUSTOM is the only way to cheat if the center circle is unbalanced...

Or RAW, of course.....