When pressing and holding a keyboard button, i.e. an a, a character pops up.

I recall that I was somehow able to change how long I need to hold a key until the Picker pops up on Yosemite. I cannot find a place to change the popup speed on Mavericks though.
defaults read -g | grep -i press does not return anything.

defaults write someoptionin Yosemite. – jottr Apr 14 '15 at 18:21