If you have registered the dissolution of the corporation, the time of registration will be considered as the end date of the fiscal year. In this case, you need to make the corporate tax declaration and payment within 3 months from the end of the month in which the registration was done.

However, if you are not undergoing a formal dissolution registration and are simply closing the corporation without registration, you should continue to follow the previous practice of making the corporate tax declaration and payment by the end of the month three months after the end of the previous fiscal year.

It's important to note that as long as the formal dissolution registration is not completed, the existing tax declaration and payment schedule should be maintained in accordance with the fiscal year's end date.

Source:

Corporate Tax Act, Article 60 (as amended on December 24, 2018)

Corporate Tax Act, Article 8 (as amended on December 24, 2018)