Electric vehicle (EV) charging management systems require scalable and standards-compliant coordination across distributed infrastructures. However, current testing approaches often lack the flexibility to support both accelerated development workflows and high-fidelity real-time validation. This paper presents a dual-mode Software-in-the-Loop (SiL) testing platform for validating EV Charging Station Management Systems (CSMSs) that communicate using the Open Charge Point Protocol (OCPP) 2.0.1. The platform enables the same CSMS software to be evaluated across discrete-time and wall-clock-time modes without modification, supporting rapid scenario testing and protocol-accurate verification. A case study involving 126 home charging stations in Denmark evaluates two smart charging strategies under real-world electricity pricing and demand conditions. Results show that discrete-time testing enables rapid performance evaluation, while wall-clock execution maintains protocol fidelity with minimal time drift. The platform offers a robust and reusable method for validating EV charging software and can support future applications involving distributed energy resources (DERs), smart grids, and cyber-physical energy systems.