How many days before the expiration of a Non-O visa can you apply for a 1-year extension in Thailand?

The application period for extending a Non-O visa can vary depending on the immigration office location in Thailand. Most offices accept applications 30 days prior to the expiration date, but some, like those in Phuket, allow applications up to 45 days in advance. It's important to check with the local immigration office as practices may differ by province.