um theres a lot of factors here..
amount of time you would practice a day?
youd probably learn faster taking lessons rather than not taking them, but not necessarily.
finding musicians to play with?
this step is crucial and will probably take you a while, if you're looking for someone decent.
also, do you wanna to be in a band just to say youre in a band?
cause it takes a lot of effort to be a good musician.
what kinda music are you trying to play? the more technical the longer it will take you to be able to play.. and so on.
especially playing metal, if you wanna be innovative and step it up.. itll take you a while.
its a plus if you have birth given talent and a natural sense of rhythm.. anwyays
give or take id say about a year or 2.. or more?