I had two 5-cell and one 6-cell on day 3 and got pregnant with a singleton so obviously one of the embryos made it to blast stage at some point. Good luck to you!!!
Just remember-all you need is one that sticks-be it 6, 8 cell, blast or not. Some couples never make it to blast, do a 3 day transfer and get pregnant.
Best of luck-I'll be thinking of you!
Usually by day 3 the embryos are 8 cells so it is unlikely they would be at a blast stageby day 5, but they may be the morula stage by then. Good luck.