It depends on the water conditions. Clean water, 1-3 weeks or so for a full tail. If he keeps on biting, there's a small chance it'll ever be full lobes again. :( Tail Biting is annoying, but harmless unless they bit too far.
Well, an ADF needs 3 gallons per frog. I'm still not sure it's fine in a 5 gallon tank. Well, there are tons of shrimp! Ghost shrimp, red cherry shrimp, amano shrimp, etc. Red cherry and ghost shrimp are better. :) Lebron ate all 4 ghost shrimp that I put in my tank so good luck!