What I'm saying is that he literally designed her. He should know her inner workings.
He designed her, but that's where what he knows stops. Just as she didn't know he had a dead man's switch, he doesn't know what modifications she might have made.
If he'd be killed one day before, would it all have been a failure? For all he knew, Uranus was going to evaporate the entire island and prevent the broadcast from happening altogether.
He knew they wouldn't do that because they needed the Mother Flame, the seraphim etc. They had to come to the island.
I don't even think the timing of the message would've mattered anyway. If he triggered the broadcast earlier, then the prediction would still be true later. Plus, I think it's save to assume the earthquake and sea level rise caused issues in places in the world, so he could've spurred people to take measures before the damage it caused.
As we saw, the only reason anyone believed him at all was that his predictions came true. Some people still didn't believe him or take it seriously like Nojiko and the Jaya pirates.
If it had been much earlier, the WG would have explained it away for the time being. They would also have the Mother Flame earlier and would have had time to hit more islands before his prediction came true. Thus making the global effects much worse.
But yes, it could've gone out earlier if he died earlier, and done some good at least.
And again, him just leaving the researchers, Sentomarou and the Vegapunks to die is pretty brutal. He also just assumed he was a good enough actor to sell himself not knowing anything, and hoped that he could keep York in the dark even though she is a genius herself and already was many steps ahead of him.
He wasn't acting, he wiped his memory.
Wouldn't he think that he was going to be assassinated soon before Lulusia happened? I thought he wanted to pass on the 'Will of Ohara', but lucky that he didn't get killed earlier for that very taboo act, before he recorded the broadcast and took measures nearly two weeks after, or everything would've been a total failure. The minute he found out he had been betrayed, the clock was ticking, and he decided to do nothing for a very long time.
Before Lulusia happened, there was no reason to send a message to the world because he didn't know it was in danger. The Ohara books are safely with Saul, so he didn't have to worry about that. He didn't make a move on York because of the aforementioned reasons.