This is the most accurate of the 2, but also most demanding on processor time and RAM requirements. It is based on creation of voronoi boundaries.
To do a single isochrone you simply click on the map. To do more than one isochrone just hold the "ctrl" key while clicking with the mouse button. To produce the isochrones hold the "shift" key down while clicking for the last Isochrone.
You define the polygon setting through the Drive Time Options menu.
An example is shown below:
