"How are you feeling?Terrific!Next silly question."

Purvis may have been gestating a queen? Hard to say since there were different experiments going on. 

Illness or congenital defects might be the easiest/best way to explain away the gestating times. Canon aside, they were almost comically fast in the AVP movies.

And Purvis was pretty funny too poor guy- "I am fine!"

 This sounds like a decent analysis

https://www.youtube.com/watch?v=dTGnooVitqs

Indeed they were lol.Less than 10 minutes it seemed.Covenant has uber fast gestation too.

I think Gestation was always just down to Plot Convenience and they NEVER had any Science/Theory to work with.

ALIENS we only got the One Chest Buster, so we could speculate the Female Host was infected the day before, but who knows HOW-LONG she had been captured before she was Face Hugged.

So with Ripley in Alien 3 it was unusually long, which i always wondered could be due to a Queen taking Longer to Gestate....  But to bring up that point about HER being Ill with some illness that has a affect on her Respiratory System and how this may be WHY the Gestation took longer is certainly Interesting and something i have NEVER considered before ;)

It seems Ripley 8 implied a Queen "a really nasty one" at 1:34

https://www.youtube.com/watch?v=PxDfECfLlF8

Ripleys queen and Purvis's chestburster do bear resemblance ..

https://youtu.be/6Z1v4FsU0Ow

https://youtu.be/zCqoA-FGgochttps://youtu.be/zCqoA-FGgoc

I've enhanced an image of Dr. Wren's face exploding when the xenomorph traveled through his head to assist the analysis ninXeno426, below.

Haha thank you kindly Ingeniero