An InventionRequiredTask is a task that contains at least one element that has never been done before and that nobody knows how to do. The effort to complete such a task is, by construction, unpredictable -- because "inventing" is a creative act that is, in a technical context, highly constrained.
Sometimes an InventionRequiredTask can take hours -- and sometimes years. InventionRequiredTask is not a synonym for "long" or "hard". The phrase characterizes the predictability of the task, not its duration or effort.
In this context, it is used in contrast to "StraightForwardTask" or "TrivialTask".
Writing a module that generates source code in an arbitrary language from a pattern definition is an InventionRequiredTask.