From Hero's Guide by JD Wiker and Rodney Thompson.

Effect: Extending a Force power allows the effects to last twice as long, at a penalty of exertion and increased difficulty. Powers with a specific time duration, such as enhance attribute or combat sense have their duration doubled. When this is used, the difficulties of the check are multiplied by 1.5 and the Jedi must make an Easy stamina check, going up +5 every time it is used, going down by -5 every hour. This is cumulative with Empower? and Enlarge Force. If the Jedi fails the check all Force powers have their difficulty doubled and the Jedi is considered fatigued until they can rest.

To learn this power, the Jedi must have 4D Control and 2D in each of the other abilities. It costs 20cp to learn, 60 without a teacher. This is an uncommon power for Jedi to teach to anyone below Master, but not unheard of.