The Boot Menu is displayed by machines with multiple versions of Windows installed, allowing the user to choose which operating system to boot into. The menu is associated with a value of 30 seconds, after which, if no user intervention is detected, the computer will boot into the default boot entry. But of course that just as various other aspects of Windows, the Boot Menu Timeout is also up for customization. Users will find that they are easily able to either increase or decrease the time-out value, via either the Boot.ini file or through bcdedit.
"If you want extra time to choose the operating system that loads on your computer, you can extend the time-out value. Or, you can shorten the time-out value so that the default operating system starts faster. For Windows Server 2003 and earlier versions of NT-based Windows, to change the boot menu time-out value in a Boot.ini file, you can use Bootcfg or edit the Boot.ini file in Notepad. To change the time-out value in EFI NVRAM, you must use Bootcfg. (Nvrboot only edits boot entries.) For Windows Vista, you can use BCDEdit to change the default boot menu time-out value", Microsoft revealed.
Essentially, for older versions of Windows, such as XP or 2003, Microsoft has limited the Boot Menu Timeout from 0 to 9999 seconds, also permitting users to add -1 for an indefinite menu display time, meaning that the machine will not boot without the user choosing the operating system. In Windows Vista the limitations are a tad more strict when it comes down to using System Configuration.
Via msconfig, users can only enter a value between 3 and 999 seconds, and the -1 value is removed completely. But of course that there is a way around this. Raymond Chen a developer on the Windows Shell team over at Microsoft, points out that you can actually go as close as 11 million seconds for the Boot Menu Timeout. In fact, some 11,059,200 seconds or 128 days. This can be done through bcdedit. Just launch cmd with elevated privileges and enter "bcdedit /timeout 11000000" in order to bypass the limitations of the msconfig tool and actually set the Boot Menu Timeout to 11 million seconds. At the same time, -1 is still unavailable, but you can go all out with a value such as 999,999,999,999 to obtain a timeout of -727,379,969. Hmm...
Set the Windows Vista Boot Menu Timeout to 11 Million Seconds
Or to 999,999,999,999 seconds