I'm of the opinion that you should wait until your tank establishes before you start dosing Excel & ferts. Just keep an eye on your plants. They'll tell you. Typically for me, it's about 2 months in before I start dosing my nano-betta tanks (I have a 3gal, 2 2gals, and a 6.6gal Betta tanks). I use clip on lights on most of them with 14W CFL spirals. I know they aren't the best lights for plants, but I'm not after super high-growth. Just happiness.
Good luck and post pictures when you can!