I created a group three days ago. It is a private group (meaning people need permission to become members) but everyone can ask to join. I specifically marked "List this group in the directory", and yet I can't find my group in a Google search.
The Google Groups directory is a separate thing from the regular Google Search. The directory is simply the listing of groups available from the Groups home page (see bullet point #9 here).
As for why your group isn't showing in Google search, it's probably just a matter of being patient: