Do I need to have 500,000 baht in my account for three months before applying for the DTV visa in Thailand?

Depends on the embassy, I applied at the Washington DC embassy and deposited the money from my business checking to my personal the day I applied. Transferred it back 10 days later after I was approved.

I just transferred a bunch of my money from different accounts into the same account a few days prior. I called the embassy and they said everything was fine. Applied and got accepted within a few hours. A couple of things to note: I've had 2 prior visas with thailand and this was in Canada. It seems that everyone has different experiences so it's a good idea to call the embassy as others have suggested. I would've been rejected with my professional portfolio without their help but they asked me to send an email and they said it would work. Sure enough it did.

There is no diffinitive answer because different embassies have different requirements. Definitely a 6 month balance of at least 500k will work, possibly a 3 month 500k balance may work, sometimes a single month with 500k will work and it's been reported a fresh balance of 500k has worked. Study up on reports from the embassy you are choosing. If you have an account with a substantial balance for 3 months or so and top it up over 500k, I'm guessing they would find you financially sound.

Call the embassy...

Embassy specific

It really varies from Embassy to Embassy, some says the amount should be in for 3 months, some requires at the time of application you should have 500K.

But if you are transferring from your own accounts, it should be okay