The citizenship rules are the same for everyone. It doesn't matter how you immigrated to Canada. Once you have become a PR, you must live in Canada for 4 years out of 6 years to qualify to apply for citizenship. So the earliest you can apply for citizenship is four years after landing in Canada and becoming a PR (assuming you haven't left Canada since landing). The processing of the citizenship application currently takes around 10 months provided you have a straight-forward application.