How much screen time should be allowed per day on mobile phone for 2-5 yr olds?

2-5 year olds should not be using the screens as a way to stimulate a distraction, in my opinion. I'd save it until they are old enough to know the uses of mobiles and electronics, and not when I can't watch over them when they're young. But if you cannot do this for some reason, I'd limit the time 60 mins a day, 20 minutes per session 3x a day during important tasks and errands I have to do that requires my full attention (making breakfast, lunch and dinner for example).