I'm told it has to be on the day. You go to the bank, make a transaction, ie put 100 baht in. Confirm that in your deposit book with an entry stamp, get your letter saying you've had 400k/800k for the time period and off you go to immigration and show that you've still got it.
Sounds like the daughter back in Thailand held a bit of sway. Many jobs in Thailand are cash in hand and difficult to prove you actually have a job to come back to. Pay slips go a long way to help with this.
Thank you for the info. I have done the marriage extension for the last nine years and found the 'hoops' very easy to get through after the first time which is a bit daunting.