If you are using a potting soil that comes with a fertilizer charge, wait two weeks. If you are using the 5:1:1 mix, you should start fertilizing right away. Some sources recommend that you wait a couple of weeks because roots DO colonize the container faster when fertility is low, but I find you need to stay on top of the N with the 5:1:1 mix. Try using a Tbsp in a 2-1/2 gallon watering can (or equal) and fertilize every weekend while the plant is growing well. Use less if it is really hot or cool.

Al