It’s now possible to create isochrone visualisations in QGIS using a new plugin by TravelTime. The plugin supports multiple modes of transport and is free to use for the first 5,000 requests per month.

Blog | TravelTime platform releases isochrone QGIS plugin
Create a QGIS isochrone using the TravelTime platform API. API keys are free to use for non-commercial purposes. You can also calculate a distance matrix and routing using the plugin.