This policy setting allows you to set the maximum amount of idle time after which the devices will automatically lock with ...

"This policy setting allows you to set the maximum amount of idle time after which the devices will automatically lock with a password. The Require Password policy setting MUST be enabled for this policy setting to take effect.  If you enable this policy setting, then you can set the amount of idle time, in minutes, after which the device automatically locks. The user must then enter the password in order to use most device functionality. The user can modify the idle timeout to be a smaller value than that specified through this policy setting, by configuring it in the Device Lock settings panel.  If you disable this policy setting, the user can set the idle timeout through the Device Lock settings panel, up to a maximum of 24 hours.  If you do not configure this policy setting, then existing password-related settings on the device remain in effect."