Depends on when they’re signing (check social media for signing times), length of creator line (the witness will let you know if they can go to next artist/writer or if they need to go back to cgc booth), and where the creator is, artist alley or main floor (witnesses are usually assigned to one area)
best advice I can give is do the ground work above (figure out where and when each person is signing before grabbing a witness) and you’ll have a very pleasant and efficient experience. Hope you have a great show !