How long is a piece of string? It really depends on what other commitments you have, and how much time each week you can dedicate to your studying.
It took me 12 months exactly. That was whilst holding down a full-time job, studying evenings and weekends. It's obviously possible to do it much quicker than that if you're not working, and it can take much longer if you have a family as well as a job.
Good luck!
FFF
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