@Vladimir *******
unless I'm not understanding it has nothing to do with how early you apply (that is a totally different parameter allowed, some offices allow you to apply 45 days before and some allow you to apply 30 days before)
The Under Consideration period given when you apply for an extension based on marriage to a thai or raising thai children is added to your current expiration date (as it is the first part of your NEXT yearly extension <- the one you're applying for).