On a multi-boot computer, during start-up, Windows will display all the operating systems which have been installed on the computer for a particular period of time, before booting into the default OS, once the default 10 second period is over. If you wish you can change this time period.
Change Time to display list of operating systems
To do so, open Computer in File Explorer. Click on System Properties.
Next click on Advanced System Settings in the left pane. This will open System Properties Advanced tab.
Next under Start and Recovery, click on the Settings button.
Under System startup, you will see the option:
Time to display list of operating systems.
Set the time to the figure you want. You may reduce it to 5 seconds if you wish.
Change Time to display Recovery Options
If you wish, you can also set the time period for which the Recovery Options are displayed. To do so, check on Time to display recovery options when needed, and change the default of 30 seconds to the time period you want.
Click on OK.
The next time you start your Windows 8 computer, you will see that the changes have taken effect.