Hi @rajanx
Interesting case. I tried re-producing this case. I shared a Pixel Perfect dashboard with a Reader user which means he only gets Viewer role.
I logged in as the Reader and I could create a schedule without an issue. So, it still appears to me as a permission issue. You are saying there are no custom permissions applied to restrict your access. So, you may have to then raise a ticket with AWS to understand what is going on behind the scene.