If you want to succeed at piano, it's best if you can find some time each day to practice, even if it's only five minutes on your busiest day.

See how much of what is written in your notebook is covered after 10 minutes at the keys. Very young beginners and very new players often find 10 minutes covers it. Going over it a second time is great for progressing quickly - even if it is at a different time on the same day. Each student learns at his or her own pace, but by around your second year of learning, around 20 minutes per day will cover most of what needs to be made ready for the next lesson. Increasing to the 'gold standard' of around 30 minutes per day as soon as you are comfortably able will ensure steady, noticeable improvement for most students. 

When you first begin, your pieces are short. This usually means getting them to sound finished doesn't take very long. At this stage make sure you pay a lot of attention to your posture (how you are sitting, and how your body is balancing and moving) and pay special attention to your hand shape. (Read the tips under How to Practice to revise this).

If you play over a few technical exercises - hand shapers, scales, broken chords, arpeggios, dozen a day, Hanon - whatever is listed currently, and go over  the pieces listed in your notebook (usually about three) you can call your practice finished.  It may take 10 minutes in your early levels, it will take more time the longer and more advanced your pieces become, and the more excited you are about becoming a better player in a shorter time.

When you are finding 20 minutes per session has become a happy habit, you can easily add in extra time on the area of practising you enjoy the most; a 'wish list' piece, or a favourite technique. 

Taking a day off somewhere in your week is often a nice balance.