This is how that change in entry stamp time worked out and it starts Oct 1st runs until Mar 31st.

As you can see ONLY the countries that get the 30 day visa EXEMPT entry are eligible for the change from 30 day to 45 day entry on Oct 1st until Mar 31st and they can get one 30 day extension on that entry stamp at the immigration office for 1900baht.

The people from the six countries that get a 30 day visa WAIVER entry are NOT part of the program and will continue to get 30 days and it cannot be extended. Those countries are Lao, Macao, Hong Kong, Mongolia Vietnam & Russia.

Also people from the 17 countries who show up here and BUY a 15 day visa on arrival for 2000baht will get 30 days visa on arrival BUT it will still cost 2000baht (They list 18 countries for VOA on that list but Saudiz get in on visa exempt now, NOT voa so it's 17)