My six year old boy goes to school in the morning. How much play time he should have with other kids, for optimal emotion and personality development?

Well, given the fact that he already goes to school, I'm sure he's already interacting with similar age kids which will help his emotional growth as well as personality development. Once back home, you can see how much time he has, especially if he has school work or other classes to attend. A good two hours' free play with other kids should be ideal though :)