Provided are various systems and processes for improving last-mile delivery of real-time, on-demand orders for perishable goods. In one aspect, a method is provided for aggregating on-demand deliveries using a depot dispatch protocol which may implement automated order transport and retrieval systems. The method comprises dispatching merchant couriers to transport on-demand orders from merchants to a merchant depot where the orders are aggregated and batched based on optimized delivery routes and destination proximities. Batches of orders are then transported to a customer depot corresponding to an area of delivery destinations. Orders are then assigned to delivery couriers for completion of delivery to customers. Such delivery routing systems and processes may be implemented alongside a delivery tracking system for generating estimated time of arrival predictive updates for real-time delivery of perishable goods. The described mechanisms improve courier efficiency, improve delivery tracking, and reduce overall delivery times.