When and how the elections are announced is entirely up to the scoutmaster.
I have been to call-outs at summer camps and district camporees. Both can be very long and troublesome for controlling younger scouts with very short attention spans. For the last several years, our troop has had its call-outs after the spring Court of Honor. We have our own ceremony team with costumes, drums, torches, etc. It has several advantages in that it is fairly short, intimate and parents can attend without traveling to camp where little Johnny sees them and says, "Hey why are my mom and dad here?".