There is no rule for a minimum number of days which you have to stay in Canada before you travel to your country. If you are not from a visa exempt country then yes you must wait for your PR card before you travel out of Canada via a commercial airline. You will not be let back into Canada without your PR card if you are not from a visa exempt country. That being said you could always go back to your home country and when your PR card arrives in the mail here in Canada you could have someone courier it to you in your home country.
If you are from a visa exempt country you can travel with your COPR. Technically an airline is not supposed to let you on the plane with only a COPR (without PR Card) but when you are from a visa exempt country the chance of them hassling you about it is very slim. Once you get back to Canada you can show immigration your COPR (or they can look you up in their computer system).