I'm pretty sure Tweek actually hatched 2 days prior to Butters since Butters didn't come out of his shell right away. I would have to check on that to be sure though. He was fully absorbed and hatched on 11/27/13. Not sure what it is with the ones that needed the extra help and weren't fully absorbed. Both of mine were/are 1/2 the size of all the others.
That's probably it then. It is possible to tell gender this young by talkativeness? If so Tweek is most definitely a female! Super chatty (hence the name Tweek LOL).
I'm picking up a pair of show quality greys on Saturday. I'm really getting spring fever.