The PR visa is usually valid for a year from the date of your medicals and you must land in Canada as a PR before that date. You don't have to move at that point though. To keep your PR, you must spend at least 730 days in Canada in your first 5 years as a PR and any rolling 5 year period after that so you can land, then leave again for up to 3 years and then move to Canada to fulfil your 730 days before your 5 years are up.
Thank You Leon! I am glad we wouldn't have to move within 3 months or so. Need lots of time to prepare. haha!