For our kids we did…
2 mornings a week at 2yo
3 mornings a week at 3yo
5 mornings a week at 4yo (pre-K)
We had (and still have) a FT nanny for the afternoons. They would come home, eat lunch, take a nap, and then go to the park. The preschool kept to the public school calendar so there were plenty of days off for outings. It worked out well.