Greg is a great one for checklists and over the years I’ve been turned into a checklist lover too. Here’s a checklist that Greg uses to see if he’s done his practice. Follow this list and you’ll never ask if you’re done practicing again!
Did you add on to what you know in a piece? Any amount is useful.
Did you work to make something you know better? What did you do?
Did you play slowly WITH A METRONOME with no stopping?
Did you think about and try to add dynamics?
Did you check your accidentals and make sure you remembered them?
Did you make sure that your articulation was correct?
Did you play for anyone?
If you can say yes to these questions then you may be done practicing! But you know what we say, you can always practice a bit more ;)