I was also wondering about this. One of the preview days is a Wednesday, and I don't know if they are doing 2 previews or 3 previews. I know a very short preview period was common at one point (Hello Dolly had 2 previews), but that was decades ago. The Normal Heart was another show racing to meet the Tony deadline, and it still had its first preview 8 days before opening (with 10 preview performances).