My question is very simple and can be understood in one line:

Is there a way, tool, etc. using Google Maps to get an overlay of all surface which is below a certain time of travel?

I hope the question is clear, but I coulnd't find anything related on the web.

If you have any information, I'll take it!

Here is what I mean illustrated by an example:

I search for a new place to live. I know the precise address of my office. I would in this case be able to overlay on Google Maps the surface which is under a certain time of travel (let's say 30 minuts by car). We would have a long surface colored around motorways (because you get faster), and colors around roads.

I think you are looking for something like Mapnificient: it shows you areas you can reach with public transportation in a given time (video).

A similar site with even more options is How Far Can I Travel. Here you can choose between inputting your speed of travel and a travel time OR a distance. Optionally, you can also specify how accurate you want the results to be.

Now, how to create such examples yourself? See this related question where the accepted answer explains step-by-step, how you can get travel time data from the Google Maps API.

Finally, for $8.75, you can buy the article Stata utilities for geocoding and generating travel time and travel distance information by Adam Ozimek and Daniel Miles that describes traveltime, a command that uses Google Maps to provide spatial information for data.

The traveltime command takes latitude and longitude information andfinds travel distances between points, as well as the time it wouldtake to travel that distance by either driving, walking, or usingpublic transportation.