You have to have active items in your store. We submit a daily feed to Froogle of all store listings. I'm not sure how often they update Froogle, it might still be once a day, but you should be able to find your listings there after 24 hours of posting them.
Google Ad Words is a paid service so it probably brings you more exposure. You'll get found based on the key words you submit to them, so it would really depend on the keywords you use and how many people perform searches in Google that would cause your submission to appear.
You could try Froogle first, then if you are interested in more exposure, look into trying Google Ad Words.
