Depends on your effort, method, resources, goals for the language, tutor and the languages you already know. I've heard of Bisayans learning in 6-8 months(or people who are already fluent in it) but if you're a native English speaker and you don't study 4-6 hours a day expect it to take a few years. Fluency is also a spectrum and it takes considerable effort to advance for example.
0-A1:1-2 months(of studying)
A1-A2:2-4 months(of studying)
A2-B1:5-6 months (of studying)
B1-B2: 10 months (of studying)
C1-C2(not even going to calculate it)
most linguists place general fluency around B1-B2, so it would take you anywhere from 18 -22 months to reach a basic level of "fluency" , assuming you have the best resources and learning method.(this isn't calculating you having some special ability to learn languages or whatever).