Once you're registered for GST, you'll need to file regular GST returns and pay GST on your taxable activities. You must file a GST return for every taxable period using the accounting basis you've chosen, even if it's a nil return.
How do I calculate and file my GST?
You cannot get an extension of time to file a GST return, so you must file it on time. A GST return is due by the 28th of the month after the end of your taxable period.