How many nights do I need to stay in Malaysia before returning to Thailand on a DTV Visa?

The official requirement is just to leave and return, there is no stated amount of time that you are required to not be in Thailand.

Some people have reported being told they need to leave Thailand for at least two nights. These reports seem to be timed with the crack down on people doing border runs. But this is at the immigration officers discretion, there isn’t anything (I believe) that they can point to that states anywhere that you need to leave for a minimum duration.

If you use an agent and are paying fees for their service then it’s likely you will have no issue. As an individual coming in and out there is always a possibility of the immigration officer stating you can’t do it same day.

You don't even need to leave the airport, can just get the next flight back. The requirement is to leave and re-enter that is all.

Exactly zero nights. You can return when you wish

There's no requirement to stay out any nights. Who told you there was?