How long before the due date can I file the 90-day report for a Non-O visa in Thailand?

You can file the 90-day report for a Non-O visa in Thailand from 15 days before the due date to 7 days after the due date. Specifically, reports can be submitted in person from exactly two weeks before up until 7 days after, online from two weeks before until the due date, and via mail if allowed by your local office, with the envelope postmarked no later than 14 days before the due date.