Split injection is widely used in conventional spark ignition engines to control mixture formation. To utilise split injection in a hydrogen direct injection engine, it is important to understand gas jet development and its variations with injection timing. This is because prolonged duration of gaseous fuel injection is required due to lower energy per volume than that of the liquid fuel, which causes complex jet-tumble interactions. The ambient air pressure and density during the gas injection also changes depending on the injection timing, adding more complexity. This study performs endoscopic high-speed imaging of gas jet laser shadowgraph in an inline four-cylinder low-pressure direct-injection spark ignition (H2LPDI) engine equipped with a side-mounted, outward opening pintle nozzle injector. Due to safety concern and its known similarity in macroscopic jet developments, helium was used as an alternative gas to hydrogen. The results showed that the gas jet development changes greatly with the split injection timing selected with respect to the intake valve closure (IVC). For pre-IVC split injection, the first jet and second jet exhibited a very similar jet structure with statistically identical spreading angle and mixture centroid because both injections occurred at low air density conditions. However, the first injection showed a higher penetration rate and jet mixing rate, suggesting a complex interplay with the intake air flow. For post-IVC split injection, the second jet showed a narrower spreading angle due to lifted lower part of the jet, suggesting a strong influence of tumble flow. As the split injection was executed after the IVC, the developing tumble flow significantly accelerated jet penetration for the first injection. However, by the time that the second injection was executed, the tumble flow structure became well defined to hinder the second jet penetration. Indeed, the mixture centroid position was more lifted for the second jet evidencing the significant influence of developing tumble flow.