'GRUB_TIMEOUT_STYLE'
     If this option is unset or set to 'menu', then GRUB will display
     the menu and then wait for the timeout set by 'GRUB_TIMEOUT' to
     expire before booting the default entry.  Pressing a key interrupts
     the timeout.

     If this option is set to 'countdown' or 'hidden', then, before
     displaying the menu, GRUB will wait for the timeout set by
     'GRUB_TIMEOUT' to expire.  If <ESC> is pressed during that time, it
     will display the menu and wait for input.  If a hotkey associated
     with a menu entry is pressed, it will boot the associated menu
     entry immediately.  If the timeout expires before either of these
     happens, it will boot the default entry.  In the 'countdown' case,
     it will show a one-line indication of the remaining time.