There’s no guarantee that the DTV will still be around in 6 months. They just flip flopped on extended visa on arrivals from 60 days back to 30. If you know you want to get one it’s better to get now even if it means wasting the first 5 or 6 months.
I’m definitely not the only one as i did it myself based on others in forums doing it with one medical appointment, of course things change and unless the embassy / consulate gives you a definitive reason there’s no knowing exactly the reason. I would do three over three months if you want.
you can email them after appointment made and request an official letter of appointment from them letting them know it’s been requested by Thai consulate