The TDM-PON is a promising candidate for mobile fronthaul due to its high scalability and cost effectiveness. Mobile fronthaul traffic has a strict one-way latency requirement of about 250μs. Therefore, latency is a critical issue for applying TDM-PON to mobile fronthaul. The traditional equal-length transmission division scheme can reduce the latency in TDM-PON. However, the scheme can still be optimized in terms of latency and bandwidth utilization. We propose a variable-length transmission division scheme to further reduce the latency in TDM-PON and improve the bandwidth utilization compared with the traditional scheme.