dear wtk:
if you are talking about bare physical practice, i agree with the others: it's non-sense.
however, if you plan to use your 9 hours to
musical practice, i encourage you very much. i would have a plan for you, btw

:
(a word before i proceed. if you are 22, don't hurry man. you have plenty of time to make your path, whatever it is.)
- from the first day, include at least one hour of music listening (not only piano: do the complete homework, and dig orchestral, vocal, chamber...well, anything you put your hands on, from medieval to 2009). also, include at least one hour to read
about music (biographies, music history, descriptive analysis). finally, one hour at least to analyse music (and study music analysis, if you need to): from roman numbers to tarasti, from schenker to meyer. the starting point, if you are not acquainted with proper analysis, is phrasing and chord-labeling. this alone will give you a very nice practice time. btw, those hours are basically
away from the piano;
- at the piano, start practicing old and not challenging repertory (islamey would be such a bad idea by now). among that, build a concert program of about an hour. then, plan your study according to your needs: if you are into the revision of satie's gymnopedies (why not?), you can play it by heart directly, with no HS or anything like that; in the other hand, if your goal is a revision of an easy beethoven sonata (opus 27/2 or opus 13 for that matter), a bit of sketchy practice would be of great benefit both to your skills and to the piece itself. the goal of that is to reach one hour a day, to play your recital straight (even if in the first days of sight-reading and remembering you'll probably take much longer. what could be funnier than playing like this?);
- after you have your recital in your belt, do two things: schedule it in a couple of venues, and start playing something harder. then, i think that you'll already (re-) developed a daily practice, so i'd assume that you will not hurt yourself trying a piece such as a ravel, or a late beethoven, or a liszt (or anything your fancy tells you). notice, please, that it's not the time yet to resume the big shots: my suggestion of late beethoven would not be opus 106 (or prokofiev's late, or anything like that). choose something, and it will probably give you from one to two hours of daily practice.
- use one hour to raw technique practice. how to do that is a very popular and controversial topic, so i will not give you any ideas. basically, do what you like to do: hanon, scales, exercises, etudes, specific parts of works, weight-lifting...well, if you are out of ideas, use the search feature of the forum, and use your hour of reading

well, that's all. the basic plan looks like that:
- listen: one hour;
- reading: one hour;
- analysis: one hour;
- recital oriented: one hour;
- new repertory: from one to two hours;
- technique specific: one hour.
you will complete your nine hours according to your needs: perhaps, another hour dedicated to the recital, or working two new pieces at a time (although i think that is misleading). anyway, keep the other advices above in mind: more than six hours a day at the piano is a complete waste of time.
best wishes!