How to know convergence time with VL6180X Time of Flight sensor with Arduino

The application scenario is to be able to calculate speed, since speed is distance divide time

The picture i uploaded is a screenshot from the datasheet. And according to the datasheet, Effective max convergence time depends on the actual convergence time plus readout averaging sample period setting. Please i want to know how to calculate the convergence time.

This is simply because i want to be able to calculate speed. Since the sensor reads distance, if i know the time, then i can calculate speed.

Or if there is a better approach to be able to calculate speed with the VL6180X sensor, please help me out.

Thank you

Convergence time .png