The buttons depend on two things: the item types on that delivery date must be shippable on the order page — in the current version gift cards, subscription plan purchases (choosing a plan), one-time fees, grab & go and venues don't get these controls — and the business settings Business: General > Allow Pickups / Allow Deliveries must each be Yes; each button is hidden individually when its method is disabled. Subscription orders show an Adjust Delivery Date link to the subscription page instead of these buttons.