The default time for an OS to automatically start is usually 30 seconds before it automatically boots up the default OS. If you have Windows 8 installed, you are greeted with a great user GUI where you can select a OS. If you want to shorten or increase the boot timeout, follow this guide
1. StepBoot to the OS menu and click Choose defaults or choose other options
2. StepClick Change the timer
3. StepSelect any of the 3 options and you are done
