Thank you for your answer.
So you think if I modify the MAX_SLEEP=60 to something bigger I will have success?
My intention is not to disable the wifi but just to keep the settings (the SSID, country code and encryption) from one use to the other, without having to set it every time I start the yun. I noticed that it takes quite a time until the yun boots.
Thank you
Edit
Everytime I boot the yun I get this message "There was a problem last time I tried configuring wireless network."
and this is the log
[ 40.960000] Error: Driver 'gpio-keys-polled' is already registered, aborting...