By default, the boot menu will display for 30 seconds before automatically selecting Windows as the boot option. You can change the delay to something shorter by following the instructions below -
1. Open the System Properties panel by right clicking "Computer" and selecting "Properties".
2. Select Advanced System Settings from the left hand menu:
3.Click the Settings button in the Start-up and Recovery group:
4. Edit the Time to display list of operating systems to suit:
You can bypass the boot menu entirely by setting this value to 0, however this is not recommended as you will no longer have a recovery feature to use if you need it.