Even though at CW you can apply for extension up to 45 days early, my experience is can only make booking up to 30 days in advance.
Yes appointments are also possible at LakSi.
Don't see why you need a 30 day extension.
You have plenty of time to apply for the Non O.. Require 15+ days remaining on your stamp and 800k in bank
Back to your appointment at CW it is possible to obtain extension at that office without appointment.
A plan that works (imo) is arrive little bit prior to 12pm in order to grab a que ticket. The break is midday to 1pm.
Note to obtain que ticket the io may ask to see your filled in TM7
In that hour do any photocopying, picture etc banking (SCB has no branch at CW) .
Photocopy and Banks located L1.
Immigration office L2
Enter immigration office (with your que ticket they let you in first)
EDIT: Just realized you are using CW to obtain non O retirement from visa exempt entry NOT the 12 month extension.
Will leave what I wrote in this post as it's general info applies to both non O and extensions.
The form you will be doing is TM87