How to get into boot menu and change the timeout.

Step 1.Navigate to settings. You can get there by hitting the gear icon on the Start menu.
Step 2.Click Update & security.
Step 3.Select Recovery from the menu
Step 4.Click Restart Now.
Step 5.Right in the boot menu, click the link Change defaults or choose other options at the bottom of the screen.
Step 6.On the next page, click Change the timer.
Step 7.Set a new timeout value to set how long the user must wait before the default OS boots automatically.