It depends on what sort of job you want to get.
Does the job require more a skill of perfection or does it require originality more than that?

In case you want to make the original idea, discuss it as much as possible with others to proof it, and try to reduce it to a mere minimum which is required to get the idea and the fun to play it. Proof whether there are several different ideas within the concept, and reduce it to one of the ideas, and make a list of every single feature or step that seems to be required, and look for steps which can be skipped to reduce the amount of work.

Do mind experiments: if you cut a certain feature or step, does the idea still work? Or does result a reduced version with a different feeling and so, but still a good concept?
Estimate the amount of time to make the game, estimate the time that you can work on it weekly, correct your estimation depending, and multiply it with 5 to get an idea how long it will take to realize the concept.