You will have to land and activate your PR before your PR visa expires. It's usually dated to expire 1 year from your medical. If you don't land in that time frame your application will be considered abandoned and you would have to re apply from the start.
After you land, you are required to meet residency obligations of a minimum of 730 days in the first 5 years from the date of landing in Canada and a minimum of 730 days at any point in the 5 preceding years after that.