We got into Tuesday's preview. It was almost full, we were told that it was a 5000 seat stadium by the cast members, who also said it would go in the rain, but not in lightning. There were a few glitches, several points where there were supposed to be explosions that didn't happen (this according to cast members afterward, who were very interested in our opinions!) It started pretty late, like around 3:20 or later I would guess, after it was supposed to start at 3:00. I think they could streamline it a little, as it lasted about 45-55 minutes (I forgot to check the time right afterward).
We were also told that the previews would last the rest of this week, but would not happen next week, while they work out what they learned this week.