Well, I think it all depends on what you are practicing. If you are working on scales and arpeggios then I say, do it all the same day until perfect. Do that for 3 hours straight or a bit less, whatever it takes so you know your fingers and where they belong in certain keys.
If you are working on practice Haydn or Bach excercises, learn the entire song the same day at a very, very slow tempo with perfect fingering as they are entirely sixteenth and eighth notes mostly. Learn the whole song that same day if just one or two pages but make sure you play every note correctly with an even, slow tempo. Wait a day, then play again and you would be surprised how you can play much faster after sleeping it through and it just stays in your brain. Don't speed up the parts you can until you learn the whole song at the same rate, then work on speeding up parts.
I hope this helps as I find when I practice, I'll play the parts I can up to speed and with so much emotion, then the parts I can't play yet sound horrible.
Distract yourself from the opening themes and jump to the next change of motion and theme in that song, practice that instead of the beginning since what you'll end up doing is learning the beginning so well that you will naturally get less practice on the middle or end of the song. I'm guilty of that so much here, now I jump around and since I know how most songs start, I go right to part 2, 3 and so on and begin learning the song from there, then learn the beginning. Try it, works for me to keep the whole structure and emphasis the same when played for a recital.