Why is hand independence so hard?
Hand independence for beginners can be QUITE the feat. ... When learning a new piece, playing with both hands may be nearly impossible at times. This is due to the technical difficulty of the piece in correlation to the technical skill of the pianist.
How long does it take to get finger independence?
If youre ONLY practicing hand independence I would say a month or two to see some real improvement. Probably closer to 3 or 4 if you're practicing other things. Don't rush it, just practice and it will come.