@Pete *********
I usually apply for another extension as soon as possible. For Bangkok 45 days in advance (day of application and last day of current extension included). The only important thing, if you need to be abroad while you on consideration stamp, you will need to buy single (in most cases) reentry, which will be valid only for consideration time and will occupy half page in passport... and of course you must return to Kingdom before consideration stamp expires and get full extension stamp in immigration on date of your appointment