I really didn't like the big change to the lore. (Surprised not to see much discussion of it here)
If you follow the series closely, the OG xenomorphs from Alien and Aliens took at least a day or two to gestate. In this movie, they can do it within an hour, I'd say. And then they can grow to full size in about the same amount of time.
The science officer mentions that they can vary their metabolism as they like, but then why take their time developing so that the adults have to stash them away in cocoons and all the rest and having to wait for the new xenos to be born.
They vary their development time according to the needs of the screenwriter and plot, I guess. Oh, the screenwriter doesn't want the crew standing around trying to figure out what to do with my host this time, I better get to bursting right away.