@Nicolas *******
there is no seasoning of the 400.000.- THB required when applying for the "change" from the tourist visa to the 90-days Non-Imm-O married-to-a-Thai-wife visa.
They money just needs to sit in your Thai bank account, and you must prove it came from abroad.
However, when up to 30 days are left on the 90-days from the visa, on the day of application to the 1-year extension of stay, the 400.000.- THB need to have seasoned in your account for two months.
NOTE: only Jomtien Immigration, in their very own interpretation of the police order, require the 2-months seasoning already for the application to the visa