Some people like to argue that within 3 days doesn't mean up to 3 days before arriving. So here goes again. . "The TDAC can be submitted online within a three-day window preceding the travel date/arriving". Hope that helps.
you can make it as difficult as you want, twisting the simplified wording that I posted. But it's really quite simple. "The TDAC can be submitted online within a three-day window preceding the travel date".
it's quite clear. Within 3 days means exactly that. It doesn't mean no later than 3 days. It says "within" those 3 days, so you have 72 hour window to submit it.