I've been in several games where the GM or players have laughed about how long it takes for things to get done. The arc looks like it was six or seven sessions where the only thing the PCs were supposed to do was cross a bridge, but in actuality the PCs found a lot of things to do in between. I've also seen GMs worry about this tendency for side quests to bog down the game or slow things down too much. I have had that fear myself. After all, if the PCs go off on too many side adventures, they might forget what is really going on in the 'main' quest. Right?
See, a table top RPG is the story you are telling with your players about what their PCs are up to in the world. As such, it's not like an RPG where the main plot of the game may awkwardly go on hold while Geralt of Rivia goes off to become the Gwent Champion of the world. Nor is there this awkward moment in the book where with time ticking down on an assassination plot, the heroes decide to become Chocobo farmers and breed exclusive and rare chocobo to race in an arena.
I mean those things can happen, but if that is what the players are happily focusing on - and you are having fun running it - then that is just what your game is doing. The world doesn't have to pause. If the PCs take too much time ignoring the machinations of the alien armada...the alien armada will move forward and advance their goals.
It doesn't matter if the PCs don't track what is going on, as long as you know what your world is up to. As long as you know what the movers and shakers on the opposition are doing then you just move them forward as they also do their thing while the PCs do their thing. If that leads to a clash? Great. If not? Oh well. But don't force the PCs into parts of the game they're not interested in, and don't be afraid to spend the time on the stuff everyone is enjoying because you're worried about losing the rest of the narrative.
Have fun with the session. Enjoy it. Enjoy the next one too. The game will happen in its time. You (probably) aren't on a limit for how many sessions you have. So enjoy it.