When at once you have registered for GST, then it is mandatory to file GST return on time, otherwise you will have to pay the penalty on daily basis.
GST registration is mandatory, if your business turn over more than 40 Lakhs.
At once GST registered, the returns will be filed on monthly basis.
If no need of GST, then you can cancel it any time.
Monthly GST return will be file each month and last date is 20th of every month.
4 returns in a year will be go as quaterly returns, that also mandatory to file.
One yearly return for each financial year is mandatory to file.