It depend on the office. Some immigration office you can transfer and the next day already start the process. Others, the money need to be there sitting for 2-3 months. If the money is there for 90 days, it will work in every office.
This is fake news. Nothing to do with agent opening 30 accounts. Agents do this all the time with every single bank. Nobody care about this. The reason why this particular time it went viral is because of what Richard said below:
"In addition to the increased restrictions on opening bank accounts now used by all banks for six months or more, the Bangkok bank in a Pattaya branch was involved in a scam with a group of 15 Chinese call center scammers involving hundreds of accounts, 2 billion baht laundering and scamming 2,000 victims."
Because as I said, every single bank are being used for quick in and out transfer. Agent put money in your account and you send back to a third account. It's done by many agents all over Thailand and with every single bank. Until the victims have money, which in this case, some rich Chinese got scammed. It made the news. So Bangkok Bank had to save face. That's it.