When should I perform my 90-day check-in for a 1-year Non-O visa in Thailand?

For your first 90-day check-in on a 1-year Multiple Entry Non-Immigrant O visa, you should report in-person to the immigration office anytime between 15 days before and 7 days after the due date. Alternatively, you can check in online 15 days before or on the due date. If you prefer using mail, ensure it is sent at least 15 days before the due date, but check if your local immigration office accepts this method.