My child did full-day kindergarten last year.
The morning was filled with learning and things that you should do in regular kindergarten. Some parents opted to pull their kids at lunchtime, similar to you.
Afternoon was filled with extra recess, snack time, extra play time, and minimal (if any) learning.
Do I think it hurt my kid to stay an extra 3 hours? I don't think so.
Did my kid enjoy the afternoons at school? I hope so.
Do I think that it helped with a transition of full day school in 1st grade? I think it did... but I don't have scientific evidence to approve.
YMMV.