Russell If you're applying for your first Non-O from inside Thailand (so you're currently on a visa exempt or tourist visa) the 800k only needs to be in a bank account on the day you apply for it. You keep 15 days left on your current stay to apply for it.
That non-O is valid for 90 days. You then need to apply for a 1 year extension. When you apply for the extension, the 800k baht needs to be in a Thai bank account for 60 days. So from the time you apply for you 1st non-O to when you apply for your yearly extension, the 800k should have already been in your account for 90 days.