In response to highly time-sensitive and dynamically emerging orders in instant delivery systems, an efficient method for order acceptance and scheduling is required. This work describes the order acceptance and scheduling problem in the instant delivery system (OAS-IDS) as a multi-trip prize collection pickup and delivery routing problem with release time and deadline time (MT-PCPDP-RT&DT). The dynamic order acceptance and scheduling problem is then decomposed into groups of continuous static problems by discretizing the scheduling horizon into several scheduling time points. An online insertion if beneficial based on trajectory similarity between orders (OIB-TSO), is proposed to tailor the order acceptance and vehicle scheduling decisions. Numerical examples indicate the OIB-TSO strategy provides a high-quality order acceptance and vehicle scheduling scheme. Management insights demonstrate the advantage and potential applicability of the designed OIB-TSO strategy in practice.