The transient response of a nanoinjection infrared photon detector was studied by exploring the relation between lateral charge transfer and jitter. The jitter of the device was measured to be 15 ps at room temperature. The jitter was almost independent of the pulse power, even after device saturation. Spatial maps for delay and amplitude were acquired. The carrier velocity was extracted from the measurements and compared with that of the simulation model. The jitter due to transit time was calculated to be in agreement with the measured data, which indicated that the jitter is primarily transit time limited.