With the 5-minute speed feature, you have a button appear that allows you to instant finish for free. This is not an item, but instead a feature for any builds that take less than 5 minutes.
When you start a 5 minute or less build, you will have the option to complete it for free.
This feature is currently available for iOS and coming soon for Android. Please just be sure you are updated to version 3.3.0 of the game.