I think you could ask the same question and get the same answer such as "How many hours per day should I practice to become a professional hockey (or baseball or basketball) player.
You have to evaluate as you go along, look at the competition, look at how your skills are improving, and then make the decision to continue or not.
To become a professional (in any endevour), I believe you would need to totally dedicate yourself. This means treating it like a job (PLUS) and be willing to devote 50+ hours per week, in learning, practicing (ie playing poker) and competing (move up in stakes once in a while to see the more experienced players)