This is the fastest method for doing drive time polygons and less demanding on processing power. The drawback is it doesn't produce as accurate results as the voronoi method and it can't create a single output layer for multiple centers with the interactive tools.
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, where the spikiness of the isochrones can also be changed.
An example is shown below:
