Of course you wait for things until they become available. But as long as the game has a pattern in how it makes you wait for things, its not waiting per se, its a rule. However, if the game makes an exception in its waiting pattern, then you ask yourself why it doesn't go according the rule that the game normally has. If the excuse is not convincing, then the waiting really becomes waiting. And well, I am sorry too, but its too bad that players ask themselves why they have to wait now, if waiting happens for a reason that does violate its own pattern. That is how it works in games.
I want to clear up a misunderstanding here. My aim is NOT to make the player sit around with nothing to do until the game allows him to, as you seem to think. Rather, I want to keep the player from being able to access the entire tech tree at the start of the game. When the event happens and the live alien research tree opens up, the player should not be done researching all the stuff he could research before the event yet. So there shouldn't be any "pointless waiting" involved.
IMHO, if we want the game to climb gradually onto higher levels, we would do better if we improve the balance of our tech-tree. Artifical delays do not create balanced progress. Making things pop up at the right time is a matter of tech-tree balance and integrity. You don't say, lets have an event here that denies access to the other branch of the tech-tree, or there will be nothing left for the later stages. You try to arrange the tech-tree in such a way that this dry-up doesn't happen. And you think twice before you ever consider a "outside" solution like an event.
You're really, really wrong about this. If this were a 4X game, I would agree, but it isn't. More on that below.
Of course the tech tree should itself provide a gradual progress through the storyline, but an outside event affecting the tech tree are plain, clean necessary in this type of game (though this particular event, I will concede, isn't).
See, its not that I have a fixation to kill this event thing 
It's really written nice and I really liked to write a built-up for it. And it's really ok for me if we prefer to go with it. But I say it bears its risks if you use events to rod-balance a tech-tree, but the game doesn't have that pattern in general. And you know, saying that the player has many other things to research meantime, is exactly the point why you force him into passiveness. You don't put a clause on other research, but when it comes to live aliens you say "my friend, you must wait a bit now, because we want't things to be interesting in this game."
It's not as if the live alien research is really holding up the player's progress through the tech tree. The technology research tree and the live alien research tree should not come together until long after the event. So the player really isn't left waiting.
I don't say it should happen when the player decides it should. And I don't say that everything should depend on the player. I say you can't just decide to make a thing "not happen" because you think the player needs to be challenged now. It's not realistic at all.
I'm saying the opposite, though. You make things happen to give the player a challenge. You make UFOs appear. You make bigger aliens appear. You make better weapons appear on the aliens' side. All this is completely unrelated to the player's progress through the tech tree (and before you argue this, it must be. Else it can and will be exploited). On higher difficulties, these "events" will happen earlier in time, giving the player less time to prepare, thus increasing the challenge (again, it's not about waiting. Time is not on the player's side!). At first glance, that might seem to be comparing apples with oranges, but it isn't. Those events, too, open up new parts of the tech tree (new weapons to research, new aliens to poke at). It's the same thing, except in this case the tech tree is opened up for free, so there's no "challenge" involved.
First things first: If we want the research to flow in a balanced way, without things drying out, we first have to try to design the tech-tree accordingly. Have appropriate research times or a prequisites structure within the tech-tree, which create the necessary "delays" in a natural way. Artificial delays such as events shouldn't be our first option to solve this issue.
Most of it will be done this way. But as I illustrated above, you can't NOT impose certain restrictions that are lifted as time passes. Because if you did, all the player would have to do is build a massive amount of labs and research the whole tech tree in a minimum amount of time. That would lead to paradoxes like X-COM having advanced alien weaponry before the aliens did. That's what I meant with my 4X comment. In X-COM games, you are always running behind on the aliens, no matter how fast you run. You can momentarily catch up, but you cannot overtake. You can do that in 4X games.
Now, with that said, there obviously will be bottlenecks, during which labs will sit idle. I'm thinking about needing a high-ranking alien commander to research, or needing to complete certain missions first. I don't think that is necessarily a bad thing. Research isn't the whole game. The tactical battles are what it's all about, and they will be plentiful, research or no research.
