This tweak is useful if you boot to the default OS most of the time and only boot to the other OS's on a limited basis.
1)Locate and Open the hidden file "boot.ini" in notepad or your favorite text editor. This file will likely be in the root directory on the boot partition of your "master" HD. For example, mine is located in "C:\boot.ini" even though I have Win98 loaded on this partition and the boot.ini file was generated when I loaded WinXP on "D:/"
2) Locate the line - timeout=30 (default is 30 seconds). Change this value to any time desired. I chose 10. Be careful not to choose too low of a setting or you may not have time to select your other OS's. Also, be careful not to change other lines as this may prevent your PC from booting at all.
3)Save the file. The next time you boot your PC, the changes will take effect.
Note: You can also adjust this in Control Panel > System > Advanced > Startup and Recovery > Settings > Time to display list of operating systems