If you're wanting to know how much you should practice piano per day, then look no further than this blog post.
For your daily practice time on piano it depends on 3 things:
The time you have to commit
How much you should practice is firstly based on your ability. If you are just starting out then this will be different to somebody who is working on their grade 8 piano.
If you are just starting out then 15-30 minutes per day is a good amount to begin at. This will be a starting point for you to practice on. This includes beginners to grade 3 level.
If you are around grade 4-5 level then around 45 minutes per day is roughly how much you should be practicing.
If you are doing grade 6-8 then trying to practice between 1 hour to 2 hours per day is a guideline of how much you should be practicing for.
Depending on what your aim is for what you want to achieve in piano practice and in your piano performance will also have an effect on how long you should be practicing for.
If you have a performance or exam coming up then it is normal to practice the piano more often so that you perform to the best of your ability.
Whereas if you are practicing for fun then you might practice less as you don't have a goal to aim for and are just practicing for fun.
For practice I think it is a good idea to have a goal for each of your practice sessions. Particularly the higher up the grades you go as this will enable you to work on the different parts of your piano playing such as technique, sight-reading, pieces, exercises and scales.
However, if you are starting out then you can work on the pieces mainly that your piano teacher is giving you.
The Time You Have To Commit
For those who are very busy and don't have a lot of time to practice this will influence the amount of time you are able to practice. Whereas if you have a lot of free time you will have more time to practice piano.
Generally the higher up the grades you go the more time you should have and therefore make available to yourself.