Ok thanksBetter suited for here, but nonetheless...
You can read about the discovery starting here (lasts for a few posts). Basically everything is fixed for the first egg (except PID, tho think this wouldn't change the inheritance) because the game overwrites the new seed with the original one every time it boots. The pokemon running in the daycare shouldn't advance the PID frame because they're running in a fixed path. The WNPCs on the route, however, definitely will. With a bit of work, it's technically abusable; however, I don't think the process is very well documented as most people just don't bother. It's been a long time since that post was made, so it's possible there's more/better resources out there now. But that's as much as I know.
Interesting why 7 frames early?Just recently did 2 egg RNGs in BW2. Exhibit A & B. You might need the beta version of PokeFinder btw.
Here are the steps btw (to rephrase the one somebody at Discord sent to me):
Step 1: Put two Pokemon in daycare
Step 2: Run around until the daycare man calls you.
Step 3: Save inside the daycare.
Step 4: Find a seed you'd like to hit in Pokefinder.
Step 5: Hit your seed and verify by using either Chatots or save spinners (since PokeFinder doesn't have Chatot support yet for Gen 5, I have to switch to RNG Reporter from here)
Step 6: Go outside, reject the egg, bike around until you have a new egg.
Step 7: Nature, IVs, & ability (I think) is determined at this point, but not shiny-ness. So if you don't want shiny, receive egg now, it will be your egg.
Step 8: If you want a shiny, it is similar to BW1 Egg RNG, where you save next to guy, open menu as fast as you can to use chatots to verify you hit seed, then receive egg 1 frame before your target frame.
In my case however, for Step 8, I have to set the encounter type to "Gift Pokemon" in RNG Reporter to see which frame is/are shiny. My target was frame 126 which is a shiny frame, but I have to hit frame 119 to hit the target.
Mod edit : Please do not double post. If you forgot to add something, please edit your previous post.