This study investigates the economic and social effects of statutory settlement cycle shortening for e-commerce platforms, applying empirical analysis and agent-based simulation models (ABM). Utilizing real-world data, industry case studies, and a structured ABM framework, the research quantifies the differentiated impacts of shortened settlement periods across platform types (principal/intermediary), scales, and financial soundness. Findings reveal that while shortening the settlement cycle provides short-term benefits—such as improved liquidity and reinvestment for small businesses—it also leads to significant long-term drawbacks: increased working capital pressure, higher financial costs, reduced investment and employment, and diminished product diversity and consumer choice. Particularly for principal-type and financially weak platforms, supplier survival rates decline and market polarization intensifies, as evidenced by rising HHI. On the consumer side, reduced product variety and higher stockouts undermine welfare, and accelerated consumer migration to overseas C-commerce platforms (e.g., AliExpress, Temu) becomes evident. The study recommends that policy design move beyond uniform regulation, calling for flexible, differentiated approaches based on platform structure, scale, and capital requirements, coupled with phased implementation, ongoing monitoring, and practical financial support. By providing an empirically validated simulation framework, this study delivers strategic implications for government policy and sustainable growth of the e-commerce ecosystem.