Funny, my son's preschool tried to make him nap when he didn't need one ... that was SO traumatic.
There is no one-size fits all answer at this age, and preschools should be flexible. Still, I understand with staffing and other concerns that they are not always able to offer a nap / no nap choice, in which case it is up to you to either select a different school, or determine what schedule will work best for your unique child.
So ... I would go with your gut, and do the shorter days.
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Mom to an amazing young adult AS son, plus an also amazing non-AS daughter. Most likely part of the "Broader Autism Phenotype" (some traits).