Unfortunately that thinking is completely incorrect. You have to provide evidence with the initial application that you've purchased coverage for a full year. It's one of the eligibility critiera to be approved. You need to buy the insurance before the application is submitted.Thank you for the reply.
During the online application it did not ask to upload a proof of medical insurance though. My parents just uploaded what they ask. We were thinking that the proof on medical insurance comes after the visa approval so that you have the exact dates for the start of insurance coverage.
https://www.canada.ca/en/immigration-refugees-citizenship/services/visit-canada/parent-grandparent-super-visa/eligibility.html