It depends on what stage of things you are in. If you are in the learning stage, as in trying to incorporate something new into your game, your practice time should be about 80% of your table time. If you are practicing to maintain your game, about 20% does fine. And if you have hit a problem you are trying to fix, shift back to that 80% until you resolve the problem.
Remember that the purpose of practice is to get better. But the purpose of all of it is so you can play the game. That's where the competition comes in. If someone spent a year, locked in their basement practicing, what would be the point? They might get really good at practicing, but so what? If you aren't playing, there is no point in practicing.
Steve