It’s impossible to give a definitive answer. The end-to-end processing timescale will depend on variables related to the personal circumstances of the applicant and their Italian spouse, such as the time needed to gather the required documentation, available appointment slots etc.
In general terms, it can take up to a year before the non-EU applicant can join their spouse in Italy, Obtaining a Nulla Osta is a pre-requisite to applying for the visa itself, and this can range from 4 to 12 months. The visa processing time is typically around three weeks, up to a couple of months, depending on where the application is made and whether any queries are raised.
Source: https://visaguide.world/europe/italy-visa/long-stay/family/