Do not change to DTV it is a inferior tourist visa, compared to a real long term visa as the non-B, which have more benefits to the longterm stay in Thailand.
Remember you may have to give up having a Thai bankaccount if you change to DTV.
If choosing to apply for DTV, many requirements such as how long the 500.000 baht should have bern in the bank is Embassy dependant, so make sure you read the Embassy website thoroughly for those requirements.
That’s why it is necessary to repeat that people should start by reading the Thai embassy website
“VISA PROCESSING TIME (4 - 5 WEEKS DURING HIGH SEASON)
Applicants are recommended to apply for the visa in advance, at least a minimum of 3 weeks and maximum 8 weeks before the expected date of your departure because the day of approval is the starting date of your visa validity.
The application will be considered only once you have completed the submission of all required documents. The Embassy reserves the right to grant an appropriate visa without prior notice.
**The Embassy will not take any responsibility if your visa is issued before/after your planned departure date because the day of approval is the starting date of your visa validity.**”