GoldenBanana, sorry for the delayed reply, though as you correctly guessed, everyone here is very busy! The reason that we are unsure as to when exactly the PID is set for Raikou/Suicune/Entei is the IV glitch which you have recognized in your post; there is no need for the collective community to know when those Pokémon specifically are generated. For the sake of completeness however, I will edit your research into the FR/LG Legendaries guide when you find the line of text when they are generated.
Now, I recognize that you have already addressed the IV glitch in your post, and are well aware that the posters here may try to dissuade you from continuing further. However, I still feel obligated to try to urge you away from this specific test. You are likely well aware that you can get a shiny Entei from HeartGold/SoulSilver, especially since you can get your SID from the Red Gyarados, so I will assume that you have already decided against doing so, and I will not pursue this further. Nonetheless, as you may notice from the various posts in the thread, it is still difficult to hit your seed and frame in FireRed/LeafGreen, and even then, the end result will be an Entei with a low Attack IV and a load of 0s as its IVs. In short, I am convinced that the amount of effort you would put into this would outweigh the eventual payoff.
In fact, I will take this opportunity to honestly say the following about FireRed/LeafGreen RNG manipulation: with the advent of Generation V Dream World abilities and a "nerfed" SelfDestruct for Mewtwo (in addition to the new "physical" Psychic move which runs off its Special Attack), it has never looked less appealing, especially given its purported difficulty. I say this not to discourage any of our current researchers, but merely to provide a realistic assessment of the situation. I would still like to see this through to the point where our users can RNG abuse for Pokémon in FireRed/LeafGreen with requisite proactivity, and as such, I commend and encourage the efforts of all our researchers.
Now, I recognize that you have already addressed the IV glitch in your post, and are well aware that the posters here may try to dissuade you from continuing further. However, I still feel obligated to try to urge you away from this specific test. You are likely well aware that you can get a shiny Entei from HeartGold/SoulSilver, especially since you can get your SID from the Red Gyarados, so I will assume that you have already decided against doing so, and I will not pursue this further. Nonetheless, as you may notice from the various posts in the thread, it is still difficult to hit your seed and frame in FireRed/LeafGreen, and even then, the end result will be an Entei with a low Attack IV and a load of 0s as its IVs. In short, I am convinced that the amount of effort you would put into this would outweigh the eventual payoff.
In fact, I will take this opportunity to honestly say the following about FireRed/LeafGreen RNG manipulation: with the advent of Generation V Dream World abilities and a "nerfed" SelfDestruct for Mewtwo (in addition to the new "physical" Psychic move which runs off its Special Attack), it has never looked less appealing, especially given its purported difficulty. I say this not to discourage any of our current researchers, but merely to provide a realistic assessment of the situation. I would still like to see this through to the point where our users can RNG abuse for Pokémon in FireRed/LeafGreen with requisite proactivity, and as such, I commend and encourage the efforts of all our researchers.