I have no musical experience what so ever.
Playing the piano (and indeed almost any musical instrument) involves three fundamental, but very different skills:
1) An understanding of basic music theory. Why do some notes (or combination of notes) sound "right" - while others sound jangly and horrible? The basics of tempo and rhthym. What it means if a song is written or played in the key of "C". Why do minor chords sound so different from major ones?
2) Developing the physical dexterity and muscle memory to play the variety of notes, and combination of notes, quickly, smoothly, and (important for pianists)
precisely the right amount of force to make your song sound right.
3) The ability to combine the previous two skills. For some people this means "sight reading" - being able to pick up a piece of sheet music and immediately start playing. For others it means being able to improvise, and create new music while sitting at the keyboard.
There is no other way of saying it: Developing the physical skills takes practice. Lots of it.You might be able to pick out simple ditties in a couple o hours, but being able to competently and musically play most sheet music will take many, many hours of practice. The amount will vary from person to person, and depends to a great extent on how focused your practice scheme is. In other words, if you keep practicing what you can already do - then you won't make progress in new areas.
Developing your knowledge of music theory is, IMHO, less "sexy" - but its equally important - especially if you have any interest in creating your own music. If you were to devote an hour a day to learning the keyboard, I'd set aside at least twenty minutes to theory and "ear training" (the ability to recognize notes and chords when you hear them).
A couple of notes on equipment: The Mac and Garageband make hooking up a digital keyboard very easy. And due to space and cost considerations this may be a better choice than a traditional piano. But if you go this route, buy the best digital keyboard you can afford: Make sure it has a physical action (the way the keys feel when you press them) that most closely mimics that of a real piano. Make sure it has full sized keys. And make sure it can accommodate an external sustain pedal. (You'll very quickly come to understand why this is important ) Lastly, if you go this route also buy a keyboard stand and bench that allow you to maintain a proper sitting posture. The way you sit and type at a computer is very, very different from the way you need to sit at a piano.