Is it still a requirement for the 800,000 Baht to be in the account for three months, for a retirement stamp renewal ?

Yes. It's three months for the second and subsequent extensions of stay.

Yes. For a retirement extension of stay using the money in a Thai bank approach, it needs to be in the bank 3 months before the day you apply for the extension except the 1st time you apply when the time requirement is only 2 months.

But if you use the combination method, even with just a small amount of embassy certified monthly income combined with money in the bank, you should avoid the 3 month requirement for the money in the bank. Emphasis on should since some offices still want 3 months even with the combination method.

Edited May 5, 201610 yr by Suradit69

Thank you both for your replies, much appreciated.