Screen time is something that should be limited for all children; at 0-2, it should be minimal or zero, as it does not support brain development in the same way that other kinds of (active) play do. It's similar to how you might learn a school subject.
Method 1: Listen to a lecture, with an overhead/projector showing some
slides.
Method 2: Listen to a shorter lecture, then answer questions about the subject
afterwards.
Method 3: Listen to a still shorter lecture, answer a few questions, and then
practice the activity for the same amount of time or more.
I think it would be easy to agree that method 3 is the best way to learn a new concept (listen, repeat, do). That's because just listening (and watching - anything passive) doesn't engage the brain in the same way that actively participating does. Completely cooperative learning is even better: you retain the memory of how to do things better.
The same applies to your child. They're learning how to do things (physical, mental, speech, etc.), and they learn best by doing. Passive content (like TV or videos on an iPad) are the worst way to do that; active content on an iPad is better, but it only can teach a limited set of skills, and unless your child is old enough to type isn't engaging them in conversation certainly. They need to be learning multiple things at once as much as possible - speech, vocabulary/grammar, emotional/social skills, motor skills. It's hard to get that from a screen; and this doesn't change as they get older (at least until a lot older). I would suggest that 2,3,6 year olds should all have the same amount of screen time per day, and so does the AAP: 1 to 2 hours per day (or less).
We have two children - almost 2 and 3.5 - and while we can't completely eliminate the almost-2 year old's screen time, we limit it to very little, probably an hour or two per week, and typically only when the older one is having screen time on the television.
For the older one, we allow no more than an hour a day, and do this largely on the iPad (which is his preference). He has 20 to 30 minutes up to twice a day (Before school and after dinner). We encourage him to use it on the toilet for one of those periods, initially as an incentive to try to poop when he was having trouble, but now as a way to allow him to be alone without his younger brother bothering him (they share a room, so it's very hard to get this alone time otherwise). He's responsible for setting a timer (we showed him how to use the iPad timer) and stopping when the timer goes off. He's not all that well behaved about stopping, but that's always difficult for children that age, and a good opportunity to work on it.
