Cat, the decision on embryo/blastocyst depends on how many embryos you have and how many you're planning to put back.
If you've got lots to choose from, and they are all developing as expected with little to choose between them, the clinic will usually leave them to day 5 to help them choose the best one(s) to put back. Some of them may stop developing on the way, some of them may develop too fast/too slow/show signs of fragmentation.
If you don't have any spares, they will put them back earlier - my clinic always said that your body is better than the highest-tech incubator, so if it's not a question of watching to see which is the best one, then they'll put them all back to give them the best chance.
I've had both experiences: with my first fresh cycle, all 5 fertilised and developed to day 5, but by then there were two that were better quality than the others, so I had one transferred and one frozen.
In my second fresh cycle, we had 4 eggs collected and they all fertilised, but on day 2, one of them hadn't divided again. By then I'd had two failed cycles so we had decided to put 3 embryos back. Because we only had 3 and were planning to transfer 3, they called me in on day 2. Hope that helps.
13.5 lining sounds like a lovely cushion for your embryos 
How are you doing, Sunrise? Are you managing to stay sane in the last few days? Sending positive vibes your way x