When you initially start to learn, your interest in playing the piano or organ is very heightened, so it is very likely you will practice a great deal more than half an hour a day and your progress will be a great deal faster. As the weeks and months go by the novelty will wear off and you may start to miss the odd days practice. This is the time you need to set a schedule for yourself, or maybe it's your child that's learning to play the piano. Now you need to be strict with yourself or your child.
Remember we started of with a minimum of half an hour a day, as a keyboard teacher I would still be asking for half an hour. Its very normal for the novelty to wear off, it's probably more common in children. So here are some tips to get you through this brief negative stage.
1. Make sure you have a piano teacher or organ teacher. Your teacher will see and hear your progress more clearly than you will and can offer encouragement and remind you of what you have achieved so far.
2. Ask yourself if you want to carry on playing the keyboard, after all, you are paying for lessons, but paying for keyboard and piano lessons is not enough, you must do the practice. I have had pupils that don't mind paying but don't want to practice at all. As far as I am concerned, they are wasting my time and are politely asked to leave and never return. (That's happened twice in thirty years as a music teacher)
3. After your half an hour practice, play the pieces of music you have already learned. This is now you're playing time, your enjoyment of what you have achieved so far.
4. Have a goal, is there a piece of sheet music you really want to play? Is there a music exam you want to pass? When I took my Grade 4 Royal Schools of Music practical exam for piano, I practiced four hours a day for six months because I wanted to pass with distinction, and I did, just. I was twelve years of age and learned a valuable lesson at that time. If you have a goal, it drives you to success.
5. If you are a parent and your child is loosing interest you have to try to encourage your child with the above suggestions, but ultimately you must insist they practice every day. (I know some people out there will disagree) If your child wont practice every day then its time to call it a day. Now I can tell you that the threat of stopping the piano lessons has worked for the majority of my pupils. I have done this myself many times with pupils and it works like a charm.
Some of my pupils from years ago are now teaching me a thing or two. They have also become teachers themselves and because they, like all music teachers, have been pupils themselves, they are very aware of the minor problems that can occur when learning to play a musical instrument such as the piano, organ or keyboard, in fact any musical instrument.
So if you want to be a keyboard player for a hobby, half an hour a day should do you. If you want to be a concert pianist then ten hours a day should just about cover it, or just start at half an hour a day and gradually evolve your practice time to what you want to do with your new talent.