I have three in that age range. DD1 spends quite a bit of time alone. She's 5, and she can read, so she spends some time every day reading, and likes to be alone to do it. Plus, she sometimes just goes and sits on her bed and plays quietly, or she'll be alone at the dining room table doing projects, and stuff like that. On days she's not at school, it might be as much as three hours a day.
The twins are 3. They spend a lot of time alone with each other, but not so much with each of them completely alone, just because they are always together. But there are periods during the day, especially when DD1 is at school, when one will play upstairs and one down, for instance. I would guess at least an hour on an average day, and probably more. But together, and away from me, it has to be at least three hours a day.
I've always strongly encouraged them to spend time alone, and to play away from me.