Every productive piano practice session is composed of several things. First, each practice session should have a specific goal in mind. Is that goal to be able to play a specific cadence of a repertoire piece successfully or to work out an intricate rhythm, or to practice technique only with exercises and scales or to work on memory? The possibilities are endless, but every piano practice session should have a goal.
Once the goal is set, make sure you know how the finished passage or exercise, or cadence will sound.
Second devise a piano practice plan. Determine how much time you will spend on specific activities or when you will let yourself move to the next challenge.
What methods will you use? How will you get to your goal - by using a metronome, by practicing rhythms away from the keyboard, by playing short sections, or by working on fingering?
Determine how you will know when you are finished for the piano practice session. Has the timer run out or are you finished when you are tired or when you have accomplished your goal.
Answer those questions and your piano practice sessions will be a sucess and it will be a joy to make music on the piano.