BG, I'm so sorry to hear about your nan. My nan passed a month before my last cycle, and I know it's particularly difficult knowing she will not see your children. My thoughts are with you and your family.

Lou, all embryos must go through a blastocyst stage to implant. It is when the cells compact and become a blast that they then become ready to hatch and then inplant. Having said that, one of my embryos made it to blast by late day 4, and was almost hatching by day 5, though more routinely they compact on day 4 (called a morula), become a blastocyst on Day 5, hatch on day 6, implant day 7. I'll PM you a link with some pictures of the various stages up to morula.