So my wife was non-O visa holder, while we were on vacation in US this summer, We applied for the DTV under “spouse of DTV holder”, around 10 days before she was due to return. Embassy in DC did not process the DTV in time so she returned to Thailand on the Non-O. A week or so later the DTV was approved.
Yesterday she flew out to KL in the morning and back in same day on DTV and no problems, non-O is done, DTV activated.
I do recommend using an agent for that first entry to ease your mind