I often get asked by parents how much should their child practise each day? This is obviously a very subjective question and you are likely to get different responses depending on who you ask. Here’s my response: it depends.
If the student is motivated to practise the piano without having someone or something to urge him/her to do so, practise as long as the student likes. I remembered that I played the piano five hours a day when I started lessons at 16 years old. Nobody forced me to do so. I simply enjoyed playing the piano. However, when I started the 2 years of preparing for my GCE A levels, I dropped to an hour a day due to time constraints. If you have unlimited time, play the piano for as long as you are able to practise effectively and efficiently. Otherwise, the extra time you spend on the piano may solidify bad habits/poor playing such as incorrect rhythms and notes.
If the student is not motivated to practise the piano or lukewarm about practising, I would suggest 5 minutes a day for 30 consecutive days. Or if that proves challenging, reduce it further. The key is to make practising the piano a habit. It is kind of like brushing your teeth, assuming that you brush it once or twice a day. Make spending the five minutes (or less) at the piano so easy that a habit is formed. Note: it is perfectly normal for the student to feel uncomfortable or resistant during the days of forming the habit. That is because new pathways in the brain need to be formed before a habit is developed. Think of a time when you want to form a habit yourself or change your ways e.g. changing your diet, changing the way you think. It is tough. So is forming the habit to practise the piano daily.
Is it absolutely necessary to practise the piano daily? No, but ideally for beginning and intermediate students, the practice should be as consistent as possible. It is unrealistic to expect that children and adults in modern societies have all the time daily to retreat to their piano. Also, I believe in a goal based practice (routine). If a student has accomplished their practice goals before their lesson, there is no real need to practice the piano. Liken that to you making a speech or presentation. If you have put in the hours to master the speech/presentation already, there’s no real need to continue to put in the hours unless you would like to further deepen your mastery of the speech/presentation.
Remember, the main objective of piano lessons or practice is enjoyment of music. However, perhaps it’s a chicken and egg conundrum. Without practice, the playing is unlikely to be ‘decent’ and it can be hard to enjoy poorly played music. Perhaps, we should strive for enjoyment of practising, which is not unlike practising for sports or other endeavours.