I have two 4 pound bunnies who get 1/4 cup of timothy pellets each day, so I would assume that a 2.5 pound bunny should get 1/8 of a cup. Your bunny should also get unlimited hay (timothy, orchard, etc.) and water. You could also considerslowly introducing veggies into the diet.
I have been giving scamper vegies and she has ate every single one. I put her on a diet last week and she seems to do pretty good. But I still need to know how much food to give her.