How many years/ days that I have to live in my principal residence to get principal residence tax exemption before selling the residence?

You must own your home for 365 consecutive days or more for it to be considered your principal residence. However, there are some exceptions, which you can see on this Canada Revenue Agency (CRA) webpage: https://www.canada.ca/en/revenue-agency/services/tax/individuals/topics/about-your-tax-return/tax-return/completing-a-tax-return/personal-income/line-12700-capital-gains/principal-residence-other-real-estate/sale-your-principal-residence.html