The short answer to your query about timing is that it takes as long as it takes. All applications are processed individually. Each couple's situation is personal to them and different from all others. Your CO will check all your evidence before making a decision, and if that involves her/him having to contact third parties, how long those people take to reply can have a bearing on the processing of your case.
That said, no doubt others whose residence has been granted recently will tell you what has happened to them - although, as I've said many times before, someone else's case is not, and cannot be, a precedent.
There can be an interview if your CO thinks it necessary, but s/he may find your evidence is convincing without that. (INZ has a duty to check partnership applications very carefully, because, as they don't require qualifications and work experience, they are the easiest target for fraudsters, who pay someone to lie about being in a relationship.)