As a word of advice, if you plan on extending your education visa at Changwattana, you better plan to lose your entire day. It took me the better part of 8 hours today. Thankfully there was a medicinal massage shop at b1 to help pass the time.
TLDR : Answer Summary
Extending an education visa at Changwattana can be a lengthy process, often taking most of the day, as experienced by a user who spent about 8 hours there. The wait may be longer after a National Holiday, but there are facilities like massage shops nearby to help pass the time.