I didn't realize that you already had your transfer. Welcome to the 2ww!
I don't know the answer to your 5 vs 6 day blast question, but each time I had a fresh transfer, they waited to see which ones made it to 6 days before freezing. I imagine that 6 is even stronger than 5, but if they're all blasts I can't imagine that it makes too much difference. I only have one frosty as a plan B back up.