Future 6G networks are expected to support net-worked collaborative robotics with stringent requirements on latency determinism, synchronization, and reliability. In current 5G systems, end-to-end latency can vary substantially because packet transmissions are not coordinated with the Time Division Duplexing (TDD) frame timing, and experimental evidence from reproducible hardware testbeds remains limited. This paper presents a testbed-based evaluation of time-slot-aware transmission in a standalone 5G system. We align packet dispatch with the 5G TDD frame structure without modifying the radio scheduler. Measurements on an OpenAirInterface-based testbed show that slot-aligned transmission improves latency determinism, reducing mean latency by up to 39.0% and jitter by up to 89.5% compared to baseline operation. These results support timing alignment as a practical mechanism for more predictable communication in cellular networks targeting collaborative robotic workloads.