Hi abs,
It's usual to have a Day 2 transfer, though some clinics will do it at Day 3. If the pick up was Monday and you transfer on Wednesday, it's a Day 2 transfer. A blastocyst (blast for short coz I'm a lazy typer) is a 5 day embryo.
All the embryos will develop at different rates, mainly becuase they don't all fertilise at the exact same moment
So on Day 2, you may get a range of 2-8 cells depending on when fertilisation took place and how quickly the more robust ones divide.
I see that you are due the same day as me! Congratulations!
love
sushee