As soon as you get married. However, be advised that if you get married as soon as she gets her PR and file for sponsorship right away, immigration will know that she was already in a serious relationship and did not tell them so you may have to prove that you did not qualify as a common law couple before she became PR. That means that you had not lived together for 12 months or more. To sponsor a spouse, you also need proof that the relationship is real so you can start thinking about what kind of proof that you will give of your relationship as well as proof of not living together.
Sponsoring a spouse will take first 39 days to approve the sponsor, see
http://www.cic.gc.ca/english/information/times/canada/process-in.asp#sponsorship and after that Islamabad average 7 months, see
http://www.cic.gc.ca/english/information/times/international/05-fc-spouses.asp#asia