What is the maximum time I can stay out of Thailand on a single exit re-entry permit with a non-O retirement visa?

The maximum time allowed outside Thailand on a single exit re-entry visa, specifically for a non-O retirement visa, is determined by the validity of your entry stamp. Your re-entry permit remains valid only until the expiration of that entry stamp, meaning you need to return to Thailand before it expires to apply for an extension. It's worth noting that a re-entry permit does not extend your overall time in Thailand; the duration of your stay continues to decrement while you are outside the country.