The number of days varies wildly from person to person, based on the complexity of their situation and application, whether additional documents are needed from them, which visa office is processing their application, etc. It's also less "number of days" and more "number of months".
The average time between AOR (CIC's official receipt of your application) and PPR (the request for you to send your passport for the visa) is 6 months, per CIC, but it takes less time for some, more time for others.
Also, there's no guarantee of a visa (permanent residency) just because you get an ITA. First you have to get your application submitted within the deadline after you get your ITA, and then CIC has to review your application and not find any grounds to refuse you - many peoples' applications get rejected due to incompleteness (missing documents) or because CIC decides that the 'evidence' they've provided is not sufficient to support their claims.