So I've tested it, here's the result.
I did this on Falcon (keep in mind that the length and duration of the roll depends on the character, so what I'm going to say only applies for Falcon).
If you're standing right below him while he bounces from the first Dair, you have:
- 8 frames of reaction time+imperfection of DJC to dair him again if he techroll behind Ness.
- 17 frames of reaction time+imperfection of DJC to dair him again if he techroll in front of Ness.
What I mean by imperfection of DJC is simply if you don't DJC the optimal way (fastest while covering enough distance). In other words, if you're frame perfect with your DJCs (which I'm sure nobody is), you have 8 frames of spared time if he techrolls behind and 17 if he techrolls in front.
Now also, go figure the differences between this:
this:
and this:
Because you're supposed to know at that frame which direction he's going if you want your full 8 and 17 frames of reaction.
If we sum up, 8 and 17 are the maximum amount of delay you can have. Now subtract the time you need to distinguish the direction, the time you need to react on it, the extra time you need to DJC because it's not perfect. I'm still positive it's not doable, but it is in theory, so I apologize for my last post.
By the way, the bet is on, which image is which tech?