As with anything, the more consistent and focused you are, the quicker you'll see results. At a minimum, we recommend using Playground once a week for an hour at a time.
However, the quality of your practice is just as important as how often you practice. When practicing, make sure to remove all distractions (TV, games, your distracting cat, etc.) so that you can really lock in and focus on what you're playing. If you do this, consistently, you'll see results in no time!