If you get married anytime after your application is submitted you can add your spouse. 1 day or 6 months,etc.
Provided this person is admissible (no medical issues, no criminality, etc), then there is no real difference.
If you get married after COPR, which is the day you become a PR, then that's a whole different story. Your application would be finalized at this moment and you couldn't add your spouse to your application. You would then have to submit an sponsorship application which is an entirely different story. You'll also need a lot more paperwork to be submitted and a very long wait ahead (1 years or more once it has been submitted)
Its impossible to predict how long this will add to your application, since you would not know how long your application would have taken otherwise. Factors such as the number of countries your spouse has lived at for over 6 months, and therefore how many police certificates are needed might be a big point.
Also, if you submit your spouse's medical upfront, that for sure will make things move faster.