If I'm approved and back to Thailand, how many days do I have to activate the DTV if my current visa is still good? And to activate it will I have to go back to the issuing country and back to Thailand again to activate?
TLDR : Answer Summary
Once you are approved for the DTV, you have 5 years from the issue date to activate it. To activate your visa, you need to exit Thailand and then re-enter the country while showing your DTV.
DTV VISA RESOURCES / SERVICES