I`m 12 and this is my 6th year of piano.
My teacher wants me to practice 45 minutes each day. How much time do you guys practice?

about 3-4 hours a day maybe sometimes more.

Also, I think it would be a good idea to give grade (if student), or if amateur or professional. Give also possibly recent pieces worked on.

This might help in answering this question too.

i just played rachmaninoffs prelude in C# minor for my last recital and im currently working on shuberts impromtu no.2 op.90

now that its summer I usually practice upwards hours (not in a straight block, usually throughout the day). I`m not exactly sure how you would define ametuer, but I`m not very advanced either.
Current peices I`m working on:

-Brahms Rhapsody in Gm
-Mendelssohn piano concerto in Gm
-A very ugly french 2 piano suite by Darius Milhaud (my brother is playing the other part, lol)
-Some random preludes and fuges from Wohl-Tempered Klavier
-Mozart Piano sonata in F (K 332)

So you see my teacher likes to have me working on several peices at once, and despite the fact that they are only moderately difficult, I have to practice that much just to get through them. But I also like practicing so anyway.

oh now that i read that more carefully, I am most certianly an amatuer as opposed to professional (i`m still a student, and don`t even consider being a professional later on)

Speaking from a teacher`s pt of view:
30 mins everyday for total beginners
45 mins everyday for advanced beg to grade 2.
1 hr everyday for grade 3 to 4.
1 and 1/2 to 2 hours for grade 5-7.
2 hours for grade 8 to PC.
Diploma and above? at least 3 hrs daily.
Professional? At least 4 to 6 hours daily.