The deadline for filing GST 3B returns varies depending on your state. Generally, dates fall on the 20th, 22nd, 24th, or 27th of the month. For example, if your turnover is above ₹5 crore, the due date might be the 20th, while for turnovers below ₹5 crore, it could be the 24th. It's crucial to check the specific date applicable to your state to ensure timely submission.