The use of the word “ceremony” in Mosiah 19:24 is puzzling, since nothing ceremonial seems to be occurring in this passage. Royal Skousen has suggested it is a scribal error, while others are argued that there is a ceremonial context for this passage. Whatever the case may be, exploring the different possibilities can yield a variety of interesting insights into this portion of the Book of Mormon.
I think there is another explanation. I think the ceremony refers to the meeting of the people who executed king Noah and Gideon’s men. The execution happened before the Gideon’s men arrived..