Usually, WB adjustment in camera is done per shooting, not per picture (exceptions exist). So it's part of the shoot preparations like selecting the right lens, ISO speed etc.
Usually I do it in the beginning and at light around the main subject. For the last Malay wedding I attended I did the WB settings according the light at / around the stage where most of the pictures will be taken with the couple.
You'll never get the WB 100% accurate for each shot but you can get a good average setting that only needs minimal additional adjustments later.