I work for a private international school, we do options of 3,4,5days a week,.
Half day or full days
Half days are 8:30- 12:30 But School/lessons start at 9am.
Full days are 8:30- 2:45pm
This is a pre school with children age 2.5-3 years
I think having 2 year olds there learning for 6 hours is too long, some of them are not out of nappies. 
Some cry for the first few weeks, Wanting there mummies. Its hard for them.