Ultra-Reliable Low-Latency Communication is a key feature of 5G, yet achieving its strict one-way latency target remains challenging in real-world deployments. While previous work proposes latency reduction techniques, most are theoretical or simulation-based and overlook practical bottlenecks in actual systems. In this paper, we analyze and optimize latency with open-source 5G RAN software. We characterize latency sources arising from 5G specifications and implementation-level factors, along with their complex interplays. Guided by this analysis, we introduce improvements reducing one way latency by 39.28 % in the downlink and 55.38 % in the uplink. Our results show the importance of system-level experimentation and provide a blueprint for advancing toward URLLC targets in both 5G and future cellular networks.