I said 10 years, but don't think it'll be much more than that.

I think the tech will be capable sooner, but big movie creations times take a while. Couple years for the tech to mature, few years where indie and cutting edge studios experiment, then a couple production lifecycles for it to be full mainstream.

Also the "substantially" criteria is going to be a tricky point, because as the AI tools get better, the less time you will need to spend interacting with them. So the time on conventional tasks decreases in absolute, but remains a high percentage because the total time needed decreases as well.

On the other hand, as AI tools make it easier to make movies, I think there will be a significant increase in both quantity and quality at the indie & amateur level.