You need to give it at least 30 days. You'll probably show that they checked your credit quicker than they report to the credit bureau.
My roommate put me as an authorized user on his account incase something happened to the house while he was away. I didn't realize that it would help my credit.. it did raise it by about 20 points or so. He's had that card for over 10 years. I just heard though, that within a year, 'piggy-backing' like this will no longer have any effect on your credit score. Credit repair companies used to pay people with good credit to sign someone with bad credit on as an AU to help raise their credit scores. Credit Bureau's found out and are going to phase that out in the coming year(s). So do your best to try and get your own and fix your credit. Otherwise, you'll end up in the situation in a year or so!
Good luck!!