Never RNGed on a 3DS myself so not sure about how much I can help. But I'll try.So. I've spent a few hours playing around with RNG reporter and I think I more or less understand what I'm meant to be doing. Some questions, though.
-I'm using a 3DS which apparently takes 8 seconds to create a seed, which is reflected in RNG reporter, but sometimes It gives me a difference of 7 seconds instead. Is this because I'm hitting the A button too quikcly? I have the 3DS synchronized to a clock by the second so I'm hitting A precisely as the second hand gets to where it is supposed to be. Is this too soon?
-Regarding timer0, I'm getting values like 167a and 167b. When RNG reporter gives me a 7 second difference in seed time I'm getting other ones though, like 1672/1678/etc. Does this mean 167a/b is the correct combination?
-The one moving NPC is the dreamyard seems to be okay as he is staying put in the same position and only turns different directions, without actually moving. I'm guessing this won't mess anything up?
- Not sure what this depends on. My guess would be that it takes 8 seconds most of the time, but it can sometimes be done in 7 seconds. If you get 8 seconds most of the time, go with that. Can't speak for the timers either.
- Timer0s tend to vary a bit. Again, I don't really have experience with using a 3DS for RNGing. None of them are the "correct" ones though as they can all be obtained, it is just a matter of finding out which one(s) you hit the most often.
- The NPC only affects the PID (Nature/shinyness/gender), not the IVs. Since you aren't after a shiny, just ignore that. If you later on should get the right IVs but the wrong nature, try advancing the PID before interacting with Latias, the easiest way is by viewing the status screen for a Chatot with a recorded Chatter.