aren't previews mostly in the middle of the week? When I registered for the guardians one, there were only weekday options for me
When we did Galaxy's Edge preview it was just before it opened to the public (8/26) It was only 3 days before it opened to the public. The next day was a press event (8/27), then another private event was held (8/28), and the opening was VERY early on 8/29.
The official park opening was 6am, but I think they let people in before 6am. It was dark out, pre-dawn.
The preview was very strict. Once you were in the land, you could roam around. I think most shops were open, but they had waits. MF:SR had a long wait, so we opted to use the single rider queue.
That's the only time I've been to Oga's and there was a wait to enter. Meh. that was one time where a truly indifferent set of cast members kinda ruined a WDW experience for us. We were seated at the bar, right in front of the CM's and nobody bothered to make eye contact or take our order. Not just us, but also the people all around us. It was odd. When a CM finally did take our orders, they had no enthusiasm of any kind, no attempt to be in character, nor even basic waitstaff politeness.
That was our first clue that Galaxy's Edge wasn't quite going to be the type of interactive experience that it was initially advertised to be.
One of the neatest things we saw that week was...well there was some sort of cosplay event at the Contemporary. We happened to be dining at CR and saw people arriving in costume for the event. We only saw a few cars arrive, but the people arriving had some very impressive cosplay costumes!