The checkout flow has no way to choose delivery timing — orders are implicitly "ASAP" and the success page shows a hardcoded "13:23 today". This adds a UI for users to choose between ASAP delivery and scheduling for a specific date/time, with Storybook stories for all new/updated UI. No backend changes needed.
Add scheduling as part of the existing "Delivery details" step (not a new step). Scheduling is a delivery concern and the current step only has 3 fields, so there's room. This avoids changing the step count, StepIndicator, or navigation logic.