Open up the /boot/grub/menu.lst file in your favorite text editor. I’m using gedit:
sudo gedit /boot/grub/menu.lstNow find the section that looks like this:
## timeout secThe timeout value is in seconds. Save the file, and when you reboot you will have that many seconds to choose the menu item you want.
# Set a timeout, in SEC seconds, before automatically booting the default entry
# (normally the first entry defined).
timeout 3