well, your last statement is the reason haha. But the reality is that you've already got a foundation set up for approval (your business). I see no reason for you to try and build an entirely new foundation centered around something you wouldn't actually do (Muay Thai). Just speaking from experience, I was very worried and impatient while waiting for my DTV. But it wasn't really all that bad, and finally a bit frictionless. You can't go wrong by providing too much in my opinion.
I did mines 7 hours before my flight. Some people did it on the plane. There's literally a kiosk (at least at DMK) to complete it there.
No urgency needed. If you wanted to really risk it, you could probably do it in the immigration line.
To answer your question. If you're set to arrive on let's say the 5th, it won't allow you to fill it out on the 1st. Needs to be 72 hours within the time of your arrival.
It does lack in terms of functionality and feature-set. Sometimes has a delay on calls. However, it gets the job done. I inform everyone that I need to communicate with, that I'll be using W.A (they're fine with it).
For business, I have a separate app for that number that works flawlessly.