There is a difference between forgetting a day of absence (which seems to be derin1010's case) or forgetting a job and/or an address where you used to live. I would encourage you to correct it via webform once you have AOR. Imagine you don't correct it, then you get a Quality Assurance questionnaire and can't produce the appropriate documents due to a mistake in your application. Always correct mistakes when you notice them.
If you have tons of buffer days and forgot a single trip, it might be a different story but your work and address history is important because it is what documents you actually having lived in Canada.