Okay...daily schedule in full day kindergarten.
8am (ish) get to school, do morning assembly or some other announcement time.
8:30am, get in class, put stuff up, bathroom time.
8:45am, circle time. Morning routine that covers the environment outside. Is it cloudy, cold, warm, snowy, rainy, outside. Is it winter, summer, spring, fall? What is the color of the week, tell me some things that are that color, etc...morning time where the whole class is involved and reviewing simple things they should all know.
9:30am. Bathroom time, hand washing, maybe morning snacks, recess, etc...
10:15/10:30. up close table time. Worksheets, basically teaching time. Could be writing, reading, pre-math, etc....classroom learning time.
11:30am get ready for lunch, set up nap time mats.
Noon, have lunch done.
12:30, back in classroom, lights off, kids down, take a nap. In Oklahoma kids under the age of 6 take naps or at least offered the opportunity to lay down and rest.
2pm, get up, straighten up room, do computer time, read books, just do stuff. 2:30 get ready to go home.
So, as you can see, the half day of kindergarten is really a straight up equal to the full day of kindergarten. Minus lunch, nap, an extra recess, and busy time until it's time to go home.
After Christmas break most kindergarten classrooms stop taking naps and they do more classwork.
If he's busy all day in pre-school it's nothing like real kindergarten through the public school. If he is doing public school pre-K he's more likely to need the full day stuff.