There are different rules regarding Italian citizenship.
For those coming from countries within the European Union, you need 4 years of uninterrupted residency (doesn’t matter if you moved from one county to another, what’s important is not to have ‘gaps’).
Those who come from outside the European Union, 10 years of uninterrupted residency is needed.
However, that’s not all. You also need to have a pristine clean criminal record and also enough financial resources to sustain yourself (which shouldn’t a problem if you have a regular job or a business registered in Italy).
As far as how long it takes to acquire it, I really couldn’t say. It depends on how each file is being processed, but in any case, it takes at least a couple years or longer.