The idea is that you should at least inform IRCC as soon as possible about your change in marital status.
I am not aware of any deadline, I'have seen some people in the forum who were given 30 days to submit these documents or so. In my case it was not like this, I was just told to submit the documents if I wished to add my spouse to my application as a dependent.
This is exactly the response I received when I used the WebForm about my change in marital status:
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Thank you for contacting Immigration, Refugees and Citizenship Canada (IRCC).
If you are the principal applicant of a permanent residence application already in process, you could add your spouse or common-law partner, dependent children, and their dependent children to your application, even if they were listed as a non-accompanying dependant in the initial application.
To do so, we invite you to send your add-on request through the
IRCC webform available on our website. You can attach the following forms and documents in the field reserved to that effect:
- A new Generic Application Form for Canada (IMM 0008) with supporting documents,
- (If applicable) A Schedule A - Background/Declaration (IMM 5669) form,
- (If applicable) An Additional Dependants/Declaration (IMM 0008DEP) form,
- (If applicable) A signed Additional Family Information (IMM 5406) form,
- A copy of the birth certificate, marriage certificate or proof of common-law relationship,
- A copy of the family member's valid passport,
- Police certificates for all countries where the family member over the age of 18 has lived for more than 6 months since turning 18,
- A letter of explanation, and
- If applicable, the proof of payment.
- Even if not requested we also submitted UP-FRONT Medical for my wife (they are not needed, but strongly recommended to avoid delays)
Useful tips
- If you need information to fill out the forms, please consult the Fill out the forms section of the instruction guide found in the application kit that you have initially used to apply.
- If the newly eligible family member is a spouse, common-law partner or dependent child who is already a permanent resident or Canadian citizen, only a copy of the birth certificate, marriage certificate or proof of common-law relationship and a letter of explanation are required.
- It may be impossible to add a member of your family to the application if a final decision has already been made.
We hope you will find this information helpful.
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The way you submit these documents is by using as many WebForms as needed. In my case it took 4. Because there is a limit in the total size of the documents (I think 3.5 MB overall) you will surely need at least a couple WebForms to do this).
Also, I would suggest that as soon as you get married to gather the documents and have them translated (if needed). Since you don't need any supporting documentation for Education or Work Experience, it should be pretty easy. It took me about 1 week (due to translations).
I took a month to do this. Even if they have finished processing your application you are okay because this would just mean they would re-open your file and assess the supporting documentation for your new dependent and then take a final decision.