I think it is better to practice for long periods of time each day. In 10-15 minutes you don't see very many results, but in one hour you will. You will progress a lot faster if you do a constant long session for two hours, than if you chop it up throughout a few days. Besides if you get good at TK, you won't want to stop because you'll be in fear that you won't be able to regain your ability.