I've already stated (in the disclaimer above) that these periods of learning could overlap - but really, I'm not entirely sure they would: clearly, you couldn't learn to play the piano after spending a few hours learning to sculpt ice (which would necessarily be a morning activity, given the lower temperatures and appropriate lighting).
And further, given Phil's professed dedication to each subject (his spending six months learning to throw cards into a hat proves an invaluable bench-mark), I don't think it likely that he would learn each thing in one long, crammed period of time. You have to remember, at the stage he is learning piano and ice sculpting, he has seemingly abandoned his desire to leave Punxsutawney, and is revelling in the infinite possibilities for self-advancement. So there.
Anyway, ignoring for a minute the good that he does, Phil does himself some badness too. Chief among them naughty activities, he robs a security van outside the bank, thanks to a Rain Man style plan:
Phil: A gust of wind. Phil: A dog barks. Phil: Cue the truck. Phil: Exit Herman; walk out into the bank. Phil: Exit Felix, and stand there with a not-so-bright look on your face. Phil: All right, Doris, come on. Hey, fix your bra, honey... That's better. Phil: Felix. Phil: How ya doin' Doris? Phil: Can I have a roll of quarters? Phil: Phil: 10, 9, 8, car... Phil: ...6, 5, quarters... Phil: ...3, 2... Herman: Felix, did I bring out two bags or one? Felix: I dunno.
That impressive knowledge, perfect to the exact minute detail, seemingly implies an extended period of research, including failed attempts (presumably also including him being run over by the car), which could not have been feasibly shorter than six weeks in my opinion. And I'm the one with the keyboard here- so six more weeks it is: Running total: 12,383 days
The final stage of this whole operation is breaking down what Phil achieves in his final Groundhog Day, and working out how long each soul-saving gesture would have taken...