For those that don't understand, this means if you go apply for an extension on Monday OR on the 26th, your extension will start on the 27th of September so there is no reasons to wait until the last minute.
TLDR : Answer Summary
This conversation discusses the specifics regarding obtaining a visa extension in Thailand as the amnesty period approaches its end on September 26th. It clarifies that applications for extensions made on either September 21st or 26th will be backdated to start on September 27th. Several comments highlight the confusion and differing experiences at immigration offices, as some applicants are advised to return closer to their expiration dates while others face complications due to COVID-related documentation. The overarching theme reflects concerns about potential overcrowding at immigration offices due to the deadline and the bureaucratic challenges faced by foreigners during this period.