It's essentially giving directions to an entire crew whose jobs are very segmented and very compartmentalized. 15 hours was average. The majority of my time was spent with the actors. Primarily just making sure the actors knew what was happening. Trainees tell the actors when to get ready in makeup and hair, in wardrobe, when to come to the set for rehearsal, when to come for shooting call and when to break for lunch.
Trainees also get to interact with the crew and act like assistant directors.
They get to set the background - working with the extras. That's another big responsibility of the assistant director. I love the fact that on my first day I didn't know what half of the words they were saying meant, but they still threw me in there. I think that's the best way to learn. I cannot emphasize the importance of good shoes.