I believe that the 30-day under consideration period starts the day my current extension expires. So it doesn't matter when you apply.
Is it possible to get an earlier start and ending to the consideration?
I will apply for a new extension of stay based on marriage to a Thai woman.
TLDR : Answer Summary
The 30-day consideration period for a visa extension based on marriage starts the day the current extension expires. It's a necessary timeframe for immigration to verify compliance with requirements. The application for a new extension can be submitted at any time, but the consideration period won't begin until the current visa is set to expire.