I just got an MT-4 I want to know the latency time and what is the latency of my old radio the HPI TF-40

I am not sure if you can find actual numbers on that. I do know from owning a MT4 that latency time decreases using a FHS3 receiver and leaving the stock one in the box. The telemetry receiver has a slower time than the next level down.

If you go to LRP site, Sanwa folder, transmiter R/C Car, MT-4, it says 4,2ms.