Under the new terms, you will need 3 years of proof you surpass the low income cut off. So it will be at least 3 years after you get your PR to apply. Years and years with the backlog.
Recent News:
Announced May 10th2013:
CIC will begin accepting new applications on January 2nd, 2014.
New Criteria:
Minimum necessary income increased by 30 percent,
Lengthen period for demonstrating funds from one year to three,
Extend sponsorship undertaking period to 20 years instead of 10,
Accompanying dependents must be 18 or younger:
http://www.cicnews.com/2013/05/parent-grandparent-sponsorship-reopen-2014-052465.html