I think that Melkor will have the opportunity to make a comment about Aulë's dwarves, and that this reaction will be very telling of his thoughts on the Children in general. It should also be the seed of orcs.
The Timing of the Awakening of the Elves has 2 major implications.
(1) Are the Valar making a pre-emptive strike to make Middle Earth safe for the coming of the Children? Or are they responding to Melkor's actions that have already hurt the Children?
and (2) Are Orcs made from Elves? Depending on how we answer that question, the timeline may not work.
I think the first point is much more crucial to the telling of this story. It has to do with the entire character of the Valar. Because Tolkien's good guys don't get to claim to be good guys just because they look the part....they have to make choices that are heroic and thoroughly grounded in 'doing the right thing' rather than the expedient thing.
So, IF the Valar are going to go to War prior to the awakening of the Children, it will almost certainly have to be because they've uncovered Melkor's plan to enslave the Children when they arrive. There would have to be an urgency of "We have to stop him!" driving them. In this scenario, the War is occurring practically on the eve of the Awakening of the Elves. They would raze Utumno because it would be thought that Melkor was going to turn that into a prison to entrap the elves (making Melkor's later words in Valinor much more....pointed). Irmo and Námo could be aware of the arrival of the Children, so that could add to the urgency - the Valar know they are 'here', and it's a race of whether Melkor or Oromë will find them first.....
I'm not sure I entirely like that idea. But it is important that there be justification for a pre-emptive strike. There has to be a reason diplomacy has failed. There has to be a reason to imprison Melkor and not leave him free to continue acting.
As for the second point...I think it best that we not answer that question. Provide plenty of hints, but leave it up to the audience to figure out where they came from. Lots of ominous sounds about how Melkor couldn't have made sentient creatures himself, so....what happened? The reasons for leaving this question unanswered should be fairly straightforward. There's no way to show it happening without
extreme levels of squick and horror, and if we imply that orcs are 'ruined' elves, it opens up all sorts of quandaries about their fate and whether or not it's okay to just kill them on sight. Much better to show Melkor's gruesome menagerie of beasts prior to the War, so we know he 'tinkers' with such things...and then leave it open. It's also a true statement that no one who wrote this history actually knew the origins of orcs. They had to deduce it after the fact, just like the audience.
[Obviously, the show creators should have some idea of 'what happened?' but it is allowed to be a complicated and involved explanation that never makes it to screen - 'Well, first he tried to breed his Maiar, but that didn't work, so then he bred monstrous beasts, but they were dumb, so then he bred the Maiar with the monstrous beasts, and that was better. He also tried forcing Maiar spirits to inhabit the beasts. Eventually, he captured some elves and added them to the mix as breeding stock, but they kept dying, so he figured out a way to animate their bodies after their spirits fled and used that.....' Like I said - ridiculously complicated.]
Also keep in mind storyteller bias - Elrond's wife was captured and tormented by orcs, badly enough that he was unable to heal her. His sons hunt orcs with unholy vengeance as a result of this incident. It's unlikely he could discuss their origins dispassionately even if he is a loremaster.
Orcs are not needed for the War. They would be completely useless against the Valar. Saving them for the return of Melkor to Middle Earth and the fight against the Noldor shouldn't be a problem. The 'older and fouler' things than orcs should dominate for now. I am fine with not seeing an orc until the Battle Under the Stars.
For a long time, we've spoken of ending Season 1 with the Elves at Cuivienen awake. I don't want to change that. Yes, I know that doesn't match the published Silmarillion, and I recognize that it introduces problems with chronology. But I think we can handle those issues.