RPM: Adjusts the range at which the user's set timing will be applied. Typically 5,000 start RPM and 20,000 end RPM is a good starting point for most motors and setups. Say there is 10 Timing Advance set as in the picture with the 5443-20,016 RPM range. This means that once the motor reaches 5443 RPM, the ESC will begin adding the 10TA. Once the motor reaches 20,016RPM the full 10TA will be applied.
To set your own RPM range, first enter an End RPM. Then click Calc RPMs and choose a start RPM from the generated list.