Some weeks ago I made a visual tool to create a bitcoin private key. The most secure way for key generation is to flip a physical coin 256 times. I flipped a coin 256 times, and made a video how to create the bitcoin private key with my tool.
Here is the video instruction:
https://youtu.be/WyBdYhwweaEThe total time just for flipping a coin was 16 minutes, plus some minutes to fill the cells in my key generator. So, the fastest way to create a safe bitcoin private key with the physical 256 coin flips is appox. 15-20 minutes.
Enjoy!

PS. The project discussion is also available here:
https://bitcointalk.org/index.php?topic=5187401.0Nice. I guess it safer to do this offline as you suggested in your other thread. And a clean or brand new pc would be more suitable for even better security.
Generating a private keys in this way can be quite intimidating. The next thing would probably be to make it easier for even a 10year old kid to generate his own private keys in this way.