This setting allows you to change the default 30 second timeout for the Startup List which normally allows you time to choose and boot an alternative operating system.
Using Windows explorer find the file called BOOT.INI on your system drive. Change the attributes of the file from read-only, by right clicking on it and choosing Properties, and then under Attributes, uncheck 'Read-only'. Then double-click on BOOT.INI and it should open in Notepad.
Under the [boot loader] section is a value called "timeout=". The number after the "=" sign is the time in seconds Windows will wait for a selection. Change the value according to the options below.
Save the file, and restart Windows for the change to take effect.
Note : The default operating system is defined with the "default=" parameter in BOOT.INI.